ThermaRest-like Foam ?
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Nick K
(nkline) - MLife

Locale: Northeast U.S.
ThermaRest-like Foam ? on 12/27/2010 07:02:07 MST Print View

Hi,

If I wanted to make an insulated inflatable sleeping pad similar to a Therm-a-Rest, which foam product would you recommend?

This sleeping pad would be used mainly in winter temperatures around freezing. Preferably, the foam would be somewhat lightweight and compactable. Or perhaps a very durable synthetic insulation instead?

Therm-a-Rest ProLite Destruction @ YouTube

Thanks!

Colin Krusor
(ckrusor) - M

Locale: Northwest US
DIY thermarest on 12/27/2010 20:45:17 MST Print View

Out of curiosity, how would you attach the face fabric to the foam? Spray adhesive? It would have to be a relatively strong bond to resist ballooning at the corners when you lay down. Keep us posted. This is an interesting idea. I'm not aware of any other attempts to make a DIY foam-core self-inflating pad.

Getting a uniform inflated thickness, and preventing ballooning, might be more problematic with fibrous insulation. You say you'd want "durable" synthetic insulation, but (if you find a way to control ballooning) I don't see how the durability (loss of loft) of the insulation is an issue in thermarest-style pads. Inflation of the pad forces the insulation to loft, due to the bond to the face fabric.

If you are content to use an inflatable pad, what led you to favor the Thermarest (fabric bonded to foam) design over a baffled, parallel-tube design (like insulated kookabay pads)?

Edited by ckrusor on 12/27/2010 20:58:05 MST.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
re on 12/28/2010 07:14:58 MST Print View

did you see this:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=24850

Nick K
(nkline) - MLife

Locale: Northeast U.S.
re: on 12/28/2010 10:12:42 MST Print View

I appreciate the comments and questions :-) I'll try to explain what I'm trying to achieve and the research I've done so far.

My body is through with 20" wide sleeping pads. It is very disappointing to have a great day in the woods and wake up the next morning feeling like somebody dragged me through a corn field due to a narrow pad. I sleep on my side with a leg kicked-out so I should have realized ahead of time that a 20" wide pad would not be adequate for me, Therm-a-Rest nor closed-cell. I recently measured the width of my usual sleeping position and it is approximately 30".

So, I thought I would try to build a 30" wide sleeping pad comfortable in temperatures from ~0-32* F.


Climashield XP/Combat

My original idea was to spray adhesive on both sides of a piece of Climashield XP or Combat and sandwich it between two layers of heat sealable fabric. This appears to be the simplest construction method. However, Bender at Kookabay.com said "I find that XP is not tough enough to be used like a self inflating mat uses foam bonded to the nylon". That led me to seek foam instead, similar to the Therm-A-Rest approach.


Open Cell Foam

In an email communication with James Atherton at Foamorder.com (see below), he recommended an open cell conventional foam and explains why in his email. He recommends their Y33 or EconoFlex C33 and explains why. However, the exact R values are unknown and their weight values for a 72" x 30 x 2" piece are:

Y33: about 1 lb per cubic foot = about 2.5 lbs for that piece
EconoFlex: about 2 lbs per cubic foot = about 5 lbs. for that piece

Two pieces of 72 x 30 4.4 oz sq yd heat sealable fabric weighs 14.66 oz or 0.915 lbs.
2.5 lbs + 0.915 lbs = 3.415 lb sleeping pad, at the very least.

Cost:
$56.70 foam
$19.14 foam shipping
$27.16 4 yards of 4.4 oz heat sealable fabric
$103 total (not including fabric shipping)
+ spray adhesive
+ ~$8 valve

An unknown R-value, approximate weight of a Therm-a-Rest Base Camp XL (4 lbs.), and higher cost of a Therm-a-Rest Base Camp XL are all discouraging reasons not to pursue this option. This might be an option, though, if foam could be purchased locally therefore eliminating shipping costs.


Therm-a-Rest Base Camp XL

The Therm-a-Rest Base Camp XL is the lightest 30" wide insulated sleeping pad I have found so far… oh, and it weighs 4 lbs.

R-value: 5
Weight: 4 lbs.
Price: $100 (~$80 on sale)


Blue closed-cell foam

Each roll is 20" wide and three rolls could be used to create two 30" wide layers.
Pro's
- easy construction
- lightweight
- inexpensive

Con's
- 3 rolls are very bulky

Unknowns
- R value


KookaBay.com Method

Heat sealable fabric is used and Bender mentioned that "the best design, although very time consuming, is to cut strips of nylon and use them as internal I beams." I am considering this method but several questions come to mind:

Can Climashield XP/Combat be used ?
If so, should it be adhered in spots (spray adhesive) ?
If using down, amount needed to be comfortable in 0-32* F ?


Time for a mental health break...

Advice is appreciated!

Nick


Email communication with James Atherton at Foamorder.com

--- first email ---

Thank you for contacting us at foamorder.com. If you are looking for a foam that will perform similarly to the Therma-A-Rest mats, this would need to be made from an open cell conventional foam. The advantage of this type of foam is that you can squeeze the air out of the foam so that it can be compacted very small and it is a light weight foam. The weakness is that you will need to use an impenetrable covering that is air tight and moisture proof. Open cell foams well absorb moisture like sponge and retain it as well. If the covering becomes punctured at all, the foam will not handle moisture well, won't compact as easily and will not do a good job of supporting a person by itself. Freezing temperatures should not affect conventional open cell foams, but they are not as insulating as closed cell foams due to the open cell nature of the material.

You can find this type of foam in the conventional foam section of our site, I would recommend you consider the EconoFlex, DuraFlex and EverFlex types: http://www.foamorder.com/cushions.html.

Closed cell foams are commonly used for camping mats. Closed cell foams have a closed cell structure that is impenetrable. Closed cell foams don't absorb moisture, don't need to be covered, are very insulating and roll up easily. However, while you can roll up a closed cell foam, you will not be able to compress/deflate it do to the closed cell nature of the material. Closed cell foams are very durable, it doesn't matter if it gets scratched or punctured, and freezing temperatures will not affect the material. Closed cell foams offer a high insulation value.

The following link will take you to our closed cell foam section, I would recommend you consider the FloTex and EVA foams: http://www.foamorder.com/closedcell.html.


--- second email ---

Thank you for your reply and for the positive feedback. While I would normally think the EconoFlex C55 would be a good choice for a 2" mat, I'm not sure how it will function for your particular application. With the design of this style mat, you will be receiving a lot of your support from the air that is trapped in the cover when it is inflated. My guess is that with the air also supporting you, this foam may feel hard although you could slightly adjust the firmness of your mat by letting air out.

I don't know the specs of the foam used in the Therma-A-Rest mats, but I would guess it is a very light weight and soft foam from my experience with this mat in the past. I double checked the weight of one of the mats for you. Based on the specs of the Base Camp 2" thick Therma-A-Rest mat, it uses a foam that is about 1.3 lbs per cubic foot. I would normally consider this a very cheap grade of foam. I would also guess the foam is oversized to help fill and maintain the shape of this mat. Rather than a 2” foam and cover being used to fill this mat, they probably used 1.75” cover with 2.0” or 2.25” of foam that is squeezed down into the covering.

Our Y33 would be closer to the weight and feel of the type of foam used in the Therma-A-Rest brand mats, although I don’t normally like recommending it because it is a very cheap grade of foam. If you are concerned about how firm the EconoFlex C55 feels, I would guess the EconoFlex C33 would be nearer the firmness of the foam used by Therma-A-Rest, perhaps even softer.

While these foams should do well for temporarily being compressed while hiking/traveling, they should not be stored for long periods of time in their compressed state. We vacuum pack these foams for shipping purposes and they can shrink up to 20% of their size when they remain in a compressed state for a prolonged period of time. I would suggest oversizing your foam a little in the thickness to help compensate for this and I think it will function better or you as well. To create a 2” thick pad, you could use a 1.75” covering with a 2.0” or 2.25” foam on the inside. If you are concerned about how the foam recovers from being compressed, you could consider better quality foams like our EverFlex V54, V44 and V34 that all recover better from compression, but the trade off is that they are heavier.

The Y33 foam weighs about 1 lb per cubic foot and your piece would weigh about 2.5 lbs.

The EconoFlex foams weigh about 2 lbs per cubic foot and your piece would weight about 5 lbs.

The EverFlex foams weigh about 3 lbs per cubic foot and would weigh about 7.5 lbs for a mat in your size.

While the foam will offer insulation value, we don't have R values nor other technical data on the insulating properties these foams. I would guess that the Y33 would be similar to the R value of the foam used in the Therma-A-Rest mat. They may increase the insulation value with the fabrics used in the covering, impermeable fabrics will help with insulation. The heavier foams would have a higher insulation value due to the greater density of the material and smaller cell structure, but I don't have a reference to offer you.

Your cost for shipping will depend on the foam you end up selecting. The EconoFlex C55 will be about $19.14 via UPS ground. I’m not sure if this item will need to be vacuum packed at $8 handling or simply tightly packed for a $3 handling fee. Our packing department will make the determination of the least expensive method of packing and shipping when they pack your item(s) so you do not incur any oversized shipping fees.

Our site is set up to quote this custom sized foam for you, offer you a shipping estimate and process your order. Here is how to use our site for the item you are considering.

1. Go to the conventional foam section: http://www.foamorder.com/cushions.html
2. Scroll down to the custom shapes and click on the one of your choice, the square/rectangle will be the first shape offered.
3. Enter your dimensions in the appropriate spaces, enter fractions as decimals.
4. Click on the price quote button.

This will generate prices in many different types of foam along with detailed descriptions (scroll down the web site quote page to read them). The site may recommend dacron wrap for your item, but this is not something I would normally recommend for the mat you are wanting to construct.

For a shipping estimate, simply enter a quantity and then place the item into the shopping cart. The site will then take you to the shopping cart feature and you will see a box for UPS, if you enter your zip code the site will give you a shipping estimate based on everything that is in your cart.

I hope you have found this information helpful. Please let me know if you have further questions.

Best Regards,
James Atherton
Product Consultant
Foamorder.com

Hours: Mon - Fri, 6 am - 2 pm (Pacific Time)
Email: Product-Info@foamorder.com
Phone: 415.503.9314
Fax: 415.349.5035

Edited by nkline on 12/28/2010 10:19:25 MST.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Pad on 12/28/2010 11:52:06 MST Print View

I guess it's still not clear to me why you are considering the self-inflating foam-core design. Simplicity?

A 30" wide, 72" long, 2-3" thick Kookabay-style pad with down or synthetic fill would weigh less than two pounds, pack up very small, and easily keep you comfortable at very cold temperatures (far below freezing, if you design it that way). You can calculate the mass of down or synthetic insulation, and the loft (pad thickness), required for your target temperature minimum by reviewing the posts on that topic in these forums. Richard Nisley's posts, in particular, are very rigorous and informative.

Nick K
(nkline) - MLife

Locale: Northeast U.S.
re: on 12/28/2010 13:56:56 MST Print View

"why you are considering the self-inflating foam-core design. Simplicity?"

Exactly. Sorry for the confusion. The Kookabay-style pad ("I-beam" construction) would probably take a lot longer to build. But, so be it if that is the best option.


"A 30" wide, 72" long, 2-3" thick Kookabay-style pad with down or synthetic fill"

I would prefer to use synthetic in this case because it is easier to work with, less expensive, and more moisture resistant. I'm still unsure of the following though:

1.) Which is the preferred synthetic insulation for this application?
The Big Agnes Insulated Air Core uses PrimaLoft Eco (good luck finding a place to buy that insulation).

2.) The insulation will be cut into strips and inserted into the tubes created by the I-beams. Should the insulation be attached via adhesive or left free-floating? Rolling-up the pad sounds like it would push or clump the insulation.

3.) What else should I be considering?


Unfortunately, I have a limited amount of cash so even though I would love to experiment, now isn't a financially appropriate time to do so. That said, a time-tested design would save frustration and $$$.

I really appreciate the help.

Nick

Edited by nkline on 12/28/2010 14:00:50 MST.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
pad on 12/28/2010 18:02:31 MST Print View

Nick,

I does seem to me that the Kookabay-style pad will be much lighter than any Thermarest-style (foam core, self inflating) pad of the same warmth. I constructed two down-filled Kookabay-style pads using 70d heat-sealable nylon from Seattle Fabrics and down from Thruhiker, and found the project very straightforward.

I felt that the two-valve system that was used on the Kookabay pads could be improved upon, and I've never been fond of Thermarest valves in general, so I used a soft, rubbery (urethane) valve that is essentially an opening with an integral, very snug fitting, cork (similar to the clear, corked valves on pool toys). I put this on the bottom face of the pad, so the weight of the user prevents the cork from popping out (there isn't really a risk of that, though; the stopper fits very tightly). Anyway, I used spray adhesive to affix a lump of climashield against the inside of the valve, to act as a filter, to prevent down from escaping. This worked very well, and the pads inflate and deflate very easily, with one valve.

I think you could do the same (fixation of synthetic insulation with spray adhesive) over a larger area, to prevent shifting of the insulation. Bonding the insulation to the fabric on both sides overcomes the issue of the poor durability (loft-maintenance) of synthetic insulation, but adds a little weight.

If you can find a valve that you're satisfied with, the project should be relatively simple.

Nick K
(nkline) - MLife

Locale: Northeast U.S.
Questions on 12/30/2010 15:29:32 MST Print View

Colin,

Thank you for sharing your experience building a Kookabay-style pad. I have decided to pursue the project but I have a few questions before I begin. I might need some "hand holding" through the process so hopefully you do not mind all my upcoming questions. Your help so far has been priceless.


Temperature Rating
0-32* F comfort range
1.) R-value needed: ~7 Do you agree?
2.) clo-value needed: ~8 Do you agree?

Those values were determined by using this chart created by Richard Nisley on 01/16/2007 at 13:31:16. I used the "Sleeping Pads Used with Speer SPE" line.


Fabric
1.) Did you use 70d heat-sealable taffeta or ripstop nylon?
2.) Is the 70d fabric thinner or thicker compared to a traditional Therm-a-rest?
3.) Would you recommend going with 200d instead?


Insulation
I am considering using 900 Fill Power White Goose Down from Thru-hiker.com. This would be my first time building gear with down.
1.) Did you use a particular method to fill the pad with the down?


I-beams
I can think of a few ways for designing the internal I-beams:
I-beam style: using two pieces of fabric
i-beam

L-style: using one piece of fabric
L-beam

Z-style: using one piece of fabric
z-beam

1.) What is your preferred design?
2.) Did you use mesh, 70d, or something else?
3.) Height and width of I-beams?
4.) How to prevent down from shifting to another chamber?
5.) Number of chambers?


Measurements
Length: 72"
Width: 30"
Depth: ~3" ?

Somewhere Richard Nisley mentioned that gear should be designed to allow down to fully loft to maximize its insulating value.
1.) Thoughts on the optimal pad depth to allow the down to loft-up?

I am trying to determine the actual amount of fabric I will need to build a pad 30" wide. It seems like the circular shape of the chambers would require that the fabric be cut wider then 30".
2.) Which shape does the pad end up taking on?

Rectangle-style pad (looking from the foot or head):
rec-style-pad

Round-style pad (looking from the foot or head):
round-style-pad

3.) Should a half-inch seam allowance be used when sealing the fabric around the edge of the pad?


Valve
My initial thoughts were to use a Therm-a-Rest Valve Kit. Your design, using a soft, rubbery urethane valve, sounds simpler and probably less expensive.

1,) Can you point me to a website that sells such valves?
2.) Which spray adhesive do you recommend for affixing a lump of climashield against the inside of the valve?


Construction Process
1.) As for sealing the heat-sealable fabric, did you use QuestOutfitters.com method 1?
2.) Any suggestions on the best order to follow (I-beams first, valve first, edge sealing last) ?


Tools
It seems like a standard cloths iron is the main tool for this project.
1.) Were there any tools you used that made the job easier?


Thank you, again, for sharing your advice and experience on this project. Happy New Year :-)

Edited by nkline on 12/30/2010 15:49:00 MST.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Pad construction on 12/30/2010 18:42:50 MST Print View

Nick,

I'll try to answer as many of your questions as I can. Maybe others reading this thread can contribute a bit of input as well. My methods may not have been the best methods.

For temperatures down to 0*F an R value of 7-8 sounds about right to me, and I'd recommend following Richard Nisley's advice wherever possible. According to Richard, if I remember right, down can be compressed about 2.5x from the "fully lofted" state without loosing much insulation value (contrary to popular belief). So, making a slightly smaller volume pad, and overfilling it a little, might actually give you a very small warmth/weight ratio advantage over a bigger pad with the same insulation (fully lofted), because the small pad uses a little less material. My pads were 2.5" thick, each with about nine ounces of down, and, based on my experience with them in the shoulder seasons, I think they would be comfortable into the single digits. This kind of thing can be pretty idiosyncratic, though.

The 70d taffeta that I used does feel a little thinner to me than the fabric from a couple of old thermarest pads I dissected a few years ago. I would definitely say that 200d fabric is not necessary, though. The 70d seems very tough. I used white 30d heat sealable ripstop fabric, also from Seattle Fabrics, for the baffle walls. I considered using the 30d for the top of the pads also (only the bottom needs to endure much abrasion) but chickened out. In retrospect I think it would have worked fine, and saved a couple of ounces. Bender, of Kookabay, makes full 30d pads occasionally and the feedback I've read suggests that they seem to hold up fine with some care (a groundsheet).

I worked for Feathered Friends for several years about a decade ago, and had to fill in as a full-time down-stuffer for about six months. For my pads I used the same method that is used at FF: I put a large plastic garbage bag of down on my scale (which has a large platform and reads 0.01g to 7kg) and pulled out down for each baffle according to my calculated amounts. I balled up the down in my fist, and making a little beak with my fingers, injected each measured ball into the appropriate baffle with a nudge from my thumb. There is a bit of vacuuming to be done afterwards, but I find this method to be simple and expedient. I haven't tried the shop-vac, sandwich bag, or cardboard tube methods.

I used 30d heat sealable ripstop for the baffle walls. I considered mesh but sewing strips of mesh to strips of heat sealable fabric and then sealing those to the face fabric seemed like a daunting task (and it might be more difficult to keep the dimensions of the pieces exact). If you decide to use heat sealable fabric for the baffle walls, I wouldn't recommend using any of the baffle-wall configurations you illustrated. The first one (I-beam) adds unnecessary weight, and the second and third configurations (L and Z configurations) aren't possible anyway because most heat sealable fabrics only seal on one side. I think it can be done two ways: pairs of mirror-image slanty C's (slanted half-I-beams), to give trapezoidal baffles, or a series of upright (non-slanty) C's (half I-beams), which gives you box baffles. I used the latter, because box baffling is lighter (uses less material) and gives a more uniform surface (and more uniform thickness):

baffle wall

-

box

I used 2.5" high baffle walls spaced 3" apart. Some people put more space between them, but that makes the thickness less consistent (thermally inefficient) and causes more narrowing of the pad due to ballooning during inflation. In other words, as you increase the space between the baffle walls, you increase the difference between max and min thickness in the inflated state, and you decrease the width of the inflated pad:

spacing

It can be seen from this figure that, using many narrow baffles, the insulation is used more efficiently (the thickness is more uniform), and you use less face fabric for the same target pad width (or, as in the figure, a wider pad with the same fabric), so you recover some of the weight penalty of the extra baffle walls.

You suggested a width of 30" in your post, and this seems very wide to me. I'm 5'11" and 160lbs and I find 20" wide enough (although I made my pads about 23" for wiggle room). My shoulders hang over the sides a tiny bit if I'm on my back, but they don't touch the ground, and my sleeping bag covers those parts (a tucked quilt would do the same). Remember when you're calculating the fabric width to take into account narrowing of the pad when it inflates. The face fabric will want to approximate hemicircles where it bridges the baffles, but your body will compress some of those, so in practice you won't actually need enough fabric to account for hemicircles in order to get your target width.

For sealing I used a small (big-spoon-sized) specialty sealing iron that I already had, set to about 325*F. I basically used Quest Outfitters Method 1, with approximately 1/2 inch seams. I sealed one edge of each baffle wall to the bottom fabric first, then flipped it over and layed it down on the top piece of fabric and sealed that, remembering to keep my C's pointed in (open toward) the direction I was progressing as I went from one baffle to the next. I sealed the outer edges last, leaving one end open for stuffing. I found that it was crucial for me to mark everything up with a sharpie beforehand so I knew where to seal. I was able to make out the slightly purplish hue of the sharpie ink against the black 70d fabric.

I don't know of a place to get the valves I used, actually. I cut them out of two old inflatable PFDs. Kite-surfing supply companies sell similar valves for inflatable-beam kites, but I think a lot of those are one-way (requiring a separate dump valve). I inflate my pads with a dry bag/inflation bag that I made for the purpose. It's just a rolltop drybag (30d heat sealable ripstop) with a short capped tube at one corner that fits snugly into the pad valves.

I hope all of this helps. Looking forward to hearing about the results. Good luck.

Edited by ckrusor on 12/31/2010 13:44:46 MST.

Steven McAllister
(brooklynkayak) - MLife

Locale: Atlantic North East
How about 25" wide? on 12/31/2010 06:38:14 MST Print View

I am also uncomfortable with 20" mattresses and with so much of my body overhanging and touching the ground, they just aren't warm enough for winter trips.

I do find the Thermarest Prolite 4 large to be adequate for me. I do get a little overhang at times, but at least I'm not touching the cold ground.

The Prolite 4 series, now called Prolite Plus or something like that is pretty warm down to maybe 20 deg. Fahrenheit. I supplement with 3/8"evazote pad when needed.

Have you tried a 25" wide mattress? They may be wide enough and would save significant weight over a 30" wide mattress.

Trying to insulate a 30" wide mattress would be heavy, but you could maybe get around this by concentrating most of the insulation towards the area around your core as that is where most of your body heat is going to radiate from. So maybe an R value of 5 in the core area and 3 everywhere else?

Prolite 4, Trail Lite, ... type mattresses in the large version can be bought used quite often and in the end would probably be cheaper than making your own.

Of course it would be a fun project to make one.

Nick K
(nkline) - MLife

Locale: Northeast U.S.
Down accumulation on 01/12/2011 19:37:00 MST Print View

Colin,

I really appreciate you taking the time to address my laundry-list of questions. Thanks so much!

How did you prevent the down from eventually accumulating into one or two baffles?

For example, when you begin inflating the pad, air blown into the pad must fill each baffle with air. My concern is that blowing action would move down from one baffle into another.

Also, did you leave space at the ends of each I-beam for air entry/exit? If so, about how much space?

Thanks again :-)

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Down shifting on 01/12/2011 22:10:53 MST Print View

Nick,

I left about three inches at each end (the deflated pad is six inches longer than the baffle walls), but didn't do anything to prevent shifting of the down. When I inflate them, I stop half way to fluff them a little and try to spread the down around. My pads would probably be a little warmer if I had been more careful about controlling the down, but it wants to fluff up and fill the space, I think. I don't think Kookabay down pads have anything to obstruct down movement, either. It's hard to tell through the 70d fabric how much clumping there is, though.

Nick K
(nkline) - MLife

Locale: Northeast U.S.
Ounces of Down Needed? on 01/17/2011 15:00:46 MST Print View

Hi Colin,

I am preparing to order the down for my pad and wanted to run some numbers by you before I order. Specifically, I am trying to determine the number of ounces of down needed.


0-32*F comfort range
R-value needed: 7-8
clo-value needed: 8-9


Ounces of Down Needed?
- 800+ fill power down: 1.68 clo/oz source
- Target: 8 R-value (9 clo-value)
9 clo value / 1.68 clo per oz = 5.35 ounces of down needed

Or, should the number of ounces of down needed be calculated by doing:
Pad dimensions: 72x30x2.5"
Pad cubic inches: 72*30*2.5 = 5,400
Ounces of Down needed: 5,400 / 800 = 6.75 ounces

I think you mentioned your pads were filled with nine ounces of down? That would give a clo-value of 15.12 (1.68 x 9) or an R-value of 13.29 (15.12 / 1.137). According to this chart your pad should be warm to at least -58*F!


I am considering ordering 800+ Fill Power Canadian Goose Down from HammockGear for $6.50/oz.

Thanks!

Edited by nkline on 01/18/2011 09:21:16 MST.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Fill weight on 01/17/2011 16:11:18 MST Print View

I overfilled my two pads. They are extremely warm. My girlfriend and I took them to South Sister in central Oregon last weekend, and camped directly on a very cold slab of bare granite. The nightime low according to my thermometer was 16*F, before the substantial wind chill, and we both found that the pads were a little too warm. I might cut the seam at a corner and remove some down from each of them.

If I were making these pads over again, I would use something closer to your numbers (5-6 oz). They should still be comfortable four-season pads at that fill weight.

I'm sure your pad will turn out really well. You'll be glad that you've been so meticulous about the details, I think. It takes some determination to be cautious and thorough when there is an urge to jump into it and produce something. I was less patient, so I'm in the more usual MYOG position of thinking that I'll make some improvements next time.

Nick K
(nkline) - MLife

Locale: Northeast U.S.
Heat Sealable Fabric on 06/16/2011 17:55:15 MDT Print View

Colin, you still out there? :-)

I am finally returning to my sleeping pad project but I have run into a problem trying to seal the heat sealable taffeta using a standard household iron.

I have been testing on small scraps of fabric, letting them cool, then trying to pull them apart to verify the bond is strong. I have noticed pockets where the bond is either very weak or no bond at all. Where a bond was formed, it's incredibly strong though. Unfortunately, the fabric is not bonding all the way through.

I am working with heat sealable taffeta ordered from Quest Outfitters in January 2011. So far I have tested the fabric with two irons at temperature settings ranging from low to high (closer to high produced a better bond) and tested on at least 40 small scraps of fabric. I verified the laminated sides were clean by wiping any dust/dirt off with a towel.

For your sleeping pad, you mentioned: "For sealing I used a small (big-spoon-sized) specialty sealing iron that I already had, set to about 325*F." Can you please tell me more about that product and where I might purchase it?

Bender mentioned he used a Harwil bar sealer. Hopefully a less expensive solution exists, though.

Any advice on how to convince this fabric to bond completely?

Thank you!

Nick

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Heat sealer on 06/16/2011 19:46:57 MDT Print View

Nicholas,

For my pads I used a hobby iron that I purchased for about $35:

iron

I like this one because it has a thermostat, not just a rheostat like a household iron. However, it is difficult to achieve a seal line of consistent width. I slid the iron along on its side to seal the baffles, and for the side seams of the pads I used a more tedious but more consistent lift-seal-lift method (using the straight edged "heel" of the iron). This worked for these pads, but it wasn't ideal.

You could also consider a rolling heat sealer like one of these:

roller

But, to be honest, I don't recommend them. It seems like such a versatile tool, but they are expensive and, in my experience, very difficult to use. They have rheostats, not thermostats, so the actual wheel temperature is always a guess. I ordered one that had an advertised temperature range of 80-410F, but I measured the wheel temperature at the lowest setting at 270F. When I wrote to inquire about this, the seller said that an 80F wheel temperature is within the range of the tool because it can be achieved when rapidly sealing a very thermally conductive plastic (?) at subzero air temperatures. So, these seem like a good idea, but I found it impossible to control. I returned mine.

I actually have a stagnating heat-sealing project right now. I'm considering buying a rolling heat sealer and rewiring it with a thermostat, but that is a complicated and expensive project. So, in short, I guess I can't really recommend any of the methods I'm familiar with.

Ryan Smith
(ViolentGreen) - F

Locale: Southeast
Re: Heat Sealable Fabric on 06/17/2011 18:30:07 MDT Print View

Nick,

From my experience, slightly less heat at a longer exposure time works better than a high heat short exposure time. I use a household iron and put the temp wheel half way between cotton & wool. I have no idea what temp this is, but it has worked great on the 2-3 pads I've made. The latest pad has had 250lbs on it for 2 weeks straight with no leaks. How long are you keeping heat on the same section of nylon?

Ryan

Nick K
(nkline) - MLife

Locale: Northeast U.S.
Setting & Exposure Times on 06/18/2011 09:17:08 MDT Print View

Thanks, Colin. I am going to play around with my iron some more and, if I am unsuccessful, I will look into using a hobby iron similar to yours.

Ryan, I am mostly using the cotton setting and have tested several exposure times: 15, 20, 25, and 30 seconds at that setting. ~20 seconds seems to produce the best bond but still not a complete bond. I also tried Quest Outfitters instructions but had the same results.

I will try a cooler setting at a longer exposure time and see what happens.

Thanks!

Dustin Short
(upalachango) - MLife
Re: Setting & Exposure Times on 06/18/2011 09:54:39 MDT Print View

Just a few things about Down:

Richard had originally stated that you can compress down up to 2.5X and it increases it's insulating value. This is "technically" correct. It's a problem of what you want to maximize though. Compressing by 2.5X increases clo value PER INCH, however it decreases clo value PER OUNCE. This was a simple oversight common when you spend so much time with a data set. Since I pointed this out to him, he's since stopped mentioning compression and him and I have emailed back and forth a bit on the subject. Everything else Richard says about insulation can be taken as holy writ as far as I can tell. His knowledge base is the closest I get to accepting implicitly.

What to take from that? Basically the practice of overfilling slightly is good. You mildly decrease the clo/oz but increase clo/inch of a project. It also has other realworld benefits that increase the performance by insuring there aren't dead spots that are devoid of down and providing a more uniform insulation layer.

As for how much you should use? You have to do some math. View each tube of your mat as a cylinder or rectangular prism (depending on your design, using baffles a rectangle will be more accurate). Then calculate the Volume in Cubic Inches (LxWxH for each tube). Divide by the down fill power (fp=cubic inches per oz), multiply by 1.10 (10% fudge factor) and you'll have your weight of down that's needed.

As far as how much down for a specific clo value, you're out of luck unfortunately. The data on loft to clo to varying fill powers is sorely lacking. I've done a lot research, scouring the few and far between research papers that mention down insulation. Few comment on the quality. From the tiny data samples I've gotten, I've found that 900fp down has anywhere from 3.5Clo/in to 4.9Clo/in. Clearly more data/research is needed to give a more accurate estimate. You're numbers of 5-6oz for 900fp makes sense. Gives you a 72x30x2.5 pad. With my loose clo/inch range you're looking at 8+ clo for the pad which should be plenty warm for your usage.

Ryan Smith
(ViolentGreen) - F

Locale: Southeast
Re: Setting & Exposure Times on 06/18/2011 12:56:43 MDT Print View

Nick-

I found that the cotton setting on my iron was too hot if I left it on the fabric for any length of time. It wanted to delaminate the coating. I think you will have better luck on a cooler setting. Let me know how it works out.

Ryan