I have been thinking about this for sometime. Some ideas are from my original poly bag DAM thread and some are from brainstorming at sub 1 lb thread. I think I may have finally joined pieces together for a durable, SUL weight DAM.

>1/8" thinlight as bottom to provide additional warmth and protection from abrasion.
>Cuben top glued to thinlight.
>Baffles made using spectra cord so the the pad doesnt balloon up when inflated.
>Down filled silk tubes inserted in the baffles.


The only thing I dont know is what kind adhesive will bond cuben to foam. But there has to a way.

How will you use the cord to make the baffles Huzefa?

Maybe the way to bond the cuben to the foam would be to use a tube of seriously sticky goop and a tack stitch. Tiger Seal is good stuff and pretty cheap. Maybe this would work for the baffles too.

How will you seal the open baffle ends, or are the down filled silk tubes (Bill F's original idea) going to be non-removeable?

If they are going to be non-removable, how will you dry them? And how will you valve the baffles?

Now that you ask I am not sure you what I have in mind can be called baffles. I mean they are not compartments just something to prevent ballooning and controlling the shape.



cords just join the cuben layer to thinlight. Think of it as a grid.

>Maybe the way to bond the cuben to the foam would be to use a tube of seriously sticky goop and a tack stitch. Tiger Seal is good stuff and pretty cheap. Maybe this would work for the baffles too.

it may work. thanks for the idea!

>How will you seal the open baffle ends, or are the down filled silk tubes (Bill F's original idea) going to be non-removeable?
yes they are going to be non removable.

>If they are going to be non-removable, how will you dry them? And how will you valve the baffles?

dry them? why?

for valve I plan to buy a inflatable pillow locally and use the valve from it.

"Why dry them"
Water is the universal solvent, it get's in everywhere somehow. If you're going to trust the impermiability of foam and cuben, you may as well save the weight (and cost) of the silk and just seal the down into the baffles with a filter under your valve.

Won't your strings have to go through the top and bottom materials? Lots of potential airleaks. Maybe the tigerseal and stitch idea may be better?

I think you'd need to seperately valve each baffle, for the reasons we discussed last time.

Let us know how it goes. ;-)

Edited by tallbloke on 07/16/2008 05:37:04 MDT.

Rog,

Silk baffle tubes serve dual purpose: 1>control the distribution of down in the pad 2> incase the pad is punctured there is no loss of down.

I have some other ideas too for DAM construction. There 3 light fabrics that I think are impermeable and will work for an inflatable pad.

>poly 2mil
Bill gave me some info on its weight. 5"flat tube weights 3.7gms/feet. so a sq yard will weight 39.96gms or 1.4oz

>silnylon
1.3-1.35 oz /sqyd. I think much more stronger and durable then poly. I remember reading somewhere that it is use in parachutes. Silicone impregnation would make it air tight.

>cuben
I think some cuben comes lighter then .3oz/sq yd I am trying to imagine how light that stuff would be but I bet I will be still be surprised when someday I actually feel it.


I think silnylon may be the way to go. If proper care is taken while use then you can use is without a shell and may be without silk baffles. Silicone sealant is cheap and easily available. I am throwing all these ideas around in the hope that someone will experiment with silnylon pad. This is an expensive project and I want to order materials only if i am sure the if it will work.

Someone with a silnylon sack and silnyon sealant can make a pillow for a very simple experiment. Colin gave me a good idea for valve. simply cut of the mouth of a soda bottle. I am hoping silicone sealant will bond silnylon to plastic bottle.

Will you use an air pump to fill the baffles?

My suspiscion is that both silnylon and cuben are so fragile that it wil take almost nothing to intorduce a small leak. Just look at the problems Sea-to-Summit have had trying to get their silnylon "dry bags" waterproof, and waterproof is much easier than air-tight. I might suggest you make a very small model to begin with, fill it with air and sit on it for a while to test if your materials and seam sealing will work.

:) thanks.

Did I mention how bored I am?

I like thinking about different ideas. Its fun. Hopefully someday I will get beyond this thinking stage and actually make something.

>Will you use an air pump to fill the baffles?
probably not. I am thinking about using a stuff sack as a pump. I have some ideas for that too.

Your suspicion may well be true. But even if I need a shell it will still be lighter then poly.

For any one who is reading this and wishing to see some results here is something you could do to help without the hassle of a valve.

Take a fully lofted down booties or balacava (If you have one) and put in a silnylon stuff sack. seal all sides with silicone sealant. Now sit on it and see if you can compress it. pls report your findings.

If there were a lighter alternative to polythene, Bill F would already be using it. Woven cloths are not airtight. Not with 60+ kilos of body on top anyway.

Bill is using a hammock so puncturing is less likely. You're idea of a closed cell foam base is good, but given the difficulty of sealing it to another material, the polytubes are still the best bet.

I've got a 6mm 1.8m x .5m pad which weighs 120g.

Given the weight Bill quoted, you are going to be up in thermarest prolite 4 territory by the time you're done. With a bit of extra warmth. Given the fragility, so built in redundancy would seem to be sensible. if you have 5 or 7 tubes and one leaks, you can live with it. If your whole mattress relies on one valve, you will get very cold when you get one puncture or valve failure.

Rog, thanks for all the great feedback.

You may be right. It is probably unlikely that Bill hasnt considered these ideas before. But I have to think it out myself in order to understand why certain things will work and certain things will not.

>if you have 5 or 7 tubes and one leaks, you can live with it. If your whole mattress relies on one valve, you will get very cold when you get one puncture or valve failure.

This is a very good point which I had not considered. I wish someone had enlightened me before.

Also while going through Bill's old post I learned that by using 5 tubes he had a 26" pad. I think I could get away with some 20" pad using just 4 tubes. That would by itself be a very light!

some calculations:
Poly at 3.7gms/feet 5feet x 4 tubes = 74 gms = 2.6oz
Plastic clips x4 =1.6oz

Bill used an ounce of down per tube of 78" lenght. I can safely assume that 60" pad would be warmer or use less down.

It seems to me that I could have a DAM probably under 10oz!

What less can I ask?

5" layflat tubing will give a tube around 3" diameter when inflated. 10"/pi
An odd number makes sense because you'd want some warmth directly under your spine.
I'd have thought 5 was the very minimum, and 7 would be better.

I'm wondering how I might heat seal a cheap space blanket into tubes along it's length.
Is Mylar heat sealable? Can it be done with a hot roller??
Would certainly need a thin pad under for puncture protection.

I was refering to an old post by Bill, see here:
http://osdir.com/ml/culture.backpacking.hammockcamping/2004-10/msg00076.html

The size is 78" long by 26" wide and is 3-1/2"
thick or loft.
...
My DAM uses 1oz of 800+Down for each baffle of its 5
Poly Tubes.

May be he was using wider tubes but he doesnt mention it.

I have no idea if space blanket is heatsealable. But you can always place them on the top of your pad. You probably dont even need it with DAM.

From BPL Thermoregulation article:

Radiative heat loss can be minimized by one of two methods. The first is by wearing a reflective barrier (such as aluminized nylon or mylar) near the skin capable of reflecting infrared radiation back to the body. The second is by wearing thick clothing (e.g., down or high-loft synthetic fill garments). The latter strategy is effective because infrared radiation cannot travel through thick insulation, and thus, most of the infrared radiation lost by the body can remain entrapped in the clothing system rather than exiting out to the environment.

Huzefa and his crazy ideas. Actually I enjoy them as they do make me think about it in a different way. Let’s see if I can help any.

Mylar is heat sealable (I’ve done it). But, it needs a higher temperature. I don’t know if your iron can go that high, maybe it can. Space blankets are aluminized Mylar (meaning they have aluminum sprayed on one side). Normal Mylar is clear and also known as PET. If you heat seal a space blanket, you have to make sure that you seal the non-aluminum sides together, or it won’t work.

The poly bags that Bill used are LDPE (I think). They require a very low temperature for heat sealing, and have a low density (compared to many other plastics).

I don’t think silnylon will work. Your stuff sack test will show one way or the other, though. I think that the silicon that is impregnated into the woven nylon will be pushed out of the way to let the pressurized air out. This is pretty high pressure (a grown man putting his entire weight on the pad). The silnylon wasn’t designed for that much pressure, only for keeping water out with no pressure difference. I also don’t think that seam sealing will keep it air tight under pressure.

I don’t know about the cuben. I know you can heat seal it because it is a PE, but how air tight is it? Can it take the pressure?

Seam sealing your compartments is doable, but I would imagine a pain in the but, even with a custom heat sealer.

I spent some time looking over Bill’s design, and thinking about your original post on this topic. I always come back to his original idea being the best. If you make it one valve for the entire pad, then you can’t take out the down and dry it. If you get a hole in one baffle, it is easily replaced with a spare.

Another thought that you and Bill might not have considered. I haven’t looked at the calculations, so I could be wrong, but hear me out anyways. I think that you could use less down for the same warmth. In a sleeping bag, the amount of down is determined by how much loft you want, and how much that weight of down will loft (ie, hold up the top fabric to form a specified volume). In the case of an inflatable bed, the down no longer needs to hold up anything, just fill the space. As long as there are no convection currents, using less down should fill the same space as more. Anyways, just some theoretical wandering.

I've tried the silnylon experiment with a Sea-to-Summit drybag, and it didn't work. I can't tell if the leak was through the fabric or through the seams. Though it did get me thinking, both in terms of your project and for my cuben quilt project, that perhaps using a drybag style of opening to inflate/deflate would be the best?

Solid info on the mylar. Thanks David.

David, glad you enjoy my crazy ideas :)

Thanks for the great feedback. Looking back I too think that Bill's original idea was best. None of my ideas could beat its simplicity.

If you want a 3.5" loft in a sleeping bag baffle and you want down to fill up 3.5" thick pad tube how is it any different? I may be wrong, but according to my understanding 'hold up the top fabric to form a specified volume' and 'just fill the space' means the same thing. Because the amount the down that is used in baffles is somewhat efficiently chosen so that when it lofts it fills up the space available in the baffles.

Edited by huzefa on 07/22/2008 04:13:53 MDT.

hey Allison. Thanks for taking out time for the experiment and reporting your findings.

drybag style of opening? I thought about it too. But then I realised that if I compress some part of quilt under me while sleeping then it should loft bag as soon as I move away from it. Otherwise I may have to get up in the middle of the night and reinflate my compressed bag. Something you should consider.

David,

Have you had any success heat sealing Cuben? The fibers are PE, but the film is PET. Cuben Corp makes a few heavier styles that use Tedlar film, but the light stuff the MYOG crowd uses is all PE fibers sandwiched between layers of 0.08 mil PET film. I tried heat sealing it but the PE fibers shrunk and deformed the material long before enough heat was applied to affect the PET film. You wrote that you know it can be done. That would be a lot cleaner and simpler than gluing and taping.

Huzefa, I don't understand what you are describing..??

post deleted and moved to appropriate thread.

sorry for the offtopic comments.

Edited by huzefa on 07/23/2008 08:36:09 MDT.

Are we talking about quilts or mattresses now?