Hi Mike

> I cut a strip of fabric and measured it wet and dry
Hum - experimental data, eh? I am going to have to try that one myself too.
(For the record, I am an *experimental* physicist, and data beats theory everyday.)

> Nylon CTE
Well, I measured it, so I believe my own data. Nylon string expanded in the cold.

> but they can't get traction because of our community's obsession with a few grams and fears
> about anything but maximal strength.
Not sure I can buy that one. For me at least, it's the elasticity of nylon which wins. I really am not fussed about small differences in strength.

Educate me some more. You are pushing very hard to replace nylon with polyester, but is there any reason to believe that PE is less environmentally damaging than nylon?

The PU vs silicone debate is over I think. PU may be cheaper, but it has been found to be a lot less reliable, weaker and shorter-life. If it gets wet it rots, and we do hear of quite a few tents being trashed that way. I am far from convinced that PU coating is an environmental match for silicone.

As for the UV degradation - it takes an AWFUL long time before a tent fly gets UV degraded - far longer than most walkers would ever experience in the field. Yes, I have tested that, and it took years of very heavy all-day use.

An interesting discussion: please continue.

Cheers

Hi Roger,
Experimental Physics - excellent!

Funny, in extreme cold I usually find that both nylon and polyester rainflies act as if they're smaller but I always attributed that to stiffness and wrinkles.

Still not with you on the inherent stretchiness of nylon vs poly nor the value of having it. Perhaps the polyester fabric you had wasn't particularly supple? The softest garment fabrics are polyester so I doubt that there's any inherent difference. I find fabric stretchiness just masks fundamental problems with pattern-fit and makes the tent flap and generally misbehave in a wind. Perhaps Ryan can add this question to his list?

The managers I have as clients only see the apparent obsession with fabric strength. It may not even exist in real life for any given customer but as an inferred attitude it's hard to miss. And you're absolutely right that UV damage really has to be extensive before a user notices - which is ANOTHER argument for lower strength materials since we don't notice until strength has dropped to a fraction (a small fraction) of new.

Polyester (PET or PETE) is what soda and water bottles are made from so there is a ready place for it in the recycling world. Recycled fleece and some sleeping bag insulations are based on it too. Nylon has no large scale recycling at present. My fabric suppliers only talk about polyesters so I take that as meaning that recycling nylons is a ways off. Full back-to-monomer-feedstock recycling has been demonstrated for both polyester and nylon. It, of course, uses much more energy and resources than mechanical repurpose-type recycling.

One commenter mentioned weight of wet fabrics. That's an easy thing to get at: the moisture absorption. Water saturated Polyester is about .5% while saturated nylon 6 runs from 4.5% to as much as 10% (with avg 8.3%). The difference is Ginormous!

Polyester ref: http://www.matweb.com/search/DataSheet.aspx?MatGUID=a696bdcdff6f41dd98f8eec3599eaa20
Nylon6 ref: http://www.matweb.com/search/DataSheet.aspx?MatGUID=726845c457b94b7cafe31d2e65739e1d

I agree that the silicone performance debate is over. I'm arguing that we shouldn't get too attached to it because it makes fabrics completely non-recyclable. It gums up the machinery and cannot be separated from the fiber. Not by any present process according to my fabric sources. Instead we should be pushing manufacturers to use some of the more advanced PUs available: water based, aliphatics and so on. The days of smelly PU that peels off are long gone (for quality brands).

Food for thought...
Best, Mike

Hi Mike

I have made and used tents from both fabrics. It may be that the coating on the polyester was much stiffer than siloxane - I think was partly polycarbonate (spinnaker), but the behavour of the tent in high wind was definitely more flappy. By tensioning the nylon fabric it seems to flap a lot less. The stretch of nylon seemed to absorb the shock loading of gusts much better too. OK, subjective assessment rather than actual measurement.

Yes, PE may be soft, but that is often more of a function of the fibre denier than the bulk material properties. Not really all that relevant to a tent, but may be so for quilts or clothing.

The hang-up over fabric strength is an amusing one. The industry has a (marketing spin) pre-occupation with 'ripstop' fabrics, but in practice the ripstop fibres do not contribute anything to fabric performance: the fabrics don't rip. But they definitely, provably reduce the water pressure rating, often badly. Get rid of the ripstop and go back to the basic plain weave and we will be ahead already.

> we should be pushing manufacturers to use some of the more advanced PUs available:
> water based, aliphatics and so on.
Ah, but how well do they perform? I am willing to believe they can be as waterproof, but what do they do to the strength of the fabric? If they can be formulated to boost the strength of the fabric as silicone does, then tell us about it. But currently PU coatings decrease the strength, which is a non-starter. Also, double coating or impregnation is now definitely preferred for performance reasons over single-sided coating.

Recycling - tricky business. I am all for it, but I have yet to see anyone suggest using PE instead of nylon for climbing ropes. Depends I guess on priorities. Mind you, if you have samples of the sorts of fabrics you are talking about, can I see them for testing? (I spent 27 years in fabric research.)

Cheers
roger@backpackinglight.com

Aha! There, that's what I'm on about:

> But currently PU coatings decrease the strength, which is a non-starter.

A non-starter even though the tear strength is more than needed? Yes, even PU coated fabrics are too strong - that's the lesson of repair departments and UV damage. This exactly fits my definition of being over-obsessed with strength. We STILL default to the lazy idea that a fabric is peachy if it's as good or better than what we've been using. I contend that the current strengths are an accident of what's been available and that they are overly strong. Getting to the bottom of what's actually needed is the essence of my request/hope for Ryan's series.

Could PU (or some other) coatings be engineered to increase tear strength? Well sure, of course. Elasticity isn't exclusive to silicone and that's the property that seems to account for the increased tear strength. We might even be able to use a silicone based coating. Anything but impregnation should be recyclable.

As lovers of the outdoors and (presumably) as environmentalists, it's non-recyclable materials that should be the non-starters, right? We should all be pushing this because it matters and is consistent with our deepest beliefs, yes?

Best, Mike

"We might even be able to use a silicone based coating. Anything but impregnation should be recyclable."

They are the same thing, coating and impregnation (at least when it comes to fabric).

The water based PU coatings were the ones most likely to dissolve and smell like puke
with exposure to water, in my experience.

"As lovers of the outdoors and (presumably) as environmentalists, it's non-recyclable materials that should be the non-starters, right? We should all be pushing this because it matters and is consistent with our deepest beliefs, yes?"

Not if you have to replace a shelter every 10 years due to coating failure or fabric
weakening. The first on the list is reduce, not recycle.

Ryan's article so far is just one big question mark. Lets see some real numbers and
tests, some videos etc.

Hi David,

I think you're mixing up water based PU with hydrolyze-able PU. They're different. Water based PU refers to using small enough PU chains that it can be held in water for depositing onto a fabric. Once there, it's the chemistry of the particular PU that determines if it decomposes with water. For the record, fabric finishers offer "water based PU" coatings that they assure me do not decay like the old PUs did. No one wants that awful old stinky stuff.

Fabric manufacturers are telling me that coatings on fabrics - even on very thin fabrics - are very different from a recycling point of view than impregnations. BTW to my knowledge, only silicone currently is impregnated into fabrics. Double sided PU coating is done for some specialty components so they can be taped on both sides but it's not a widespread material so I can't speak to its recyclability - yet.

I hope I don't sound like I'm arguing for short lived tents. Absolutely not. But we keep falling into the rhetorical mode that anything less than what we have now is unacceptable even though we have no actual basis for comparison. Why, for instance would you assume that a PU coated tent only lasts 10 years when there are a heck of a lot of that type of tent out there now which are already in their second decade of use?

Still, just to be ideologically clear I'm going to climb out onto this theoretical branch: I contend that a tent that lasts 20 years but has no way to be recycled is not better than a tent that last 10 years but is 100% recycled. I'm suggesting that any non-recyclable product is backward in just that way despite whatever else it may have going for it. It's non-optimal and we should strive to AVOID IT OR FIX IT.

Best, Mike

"I think you're mixing up water based PU with hydrolyze-able PU. They're different. Water based PU refers to using small enough PU chains that it can be held in water for depositing onto a fabric. Once there, it's the chemistry of the particular PU that determines if it decomposes with water. For the record, fabric finishers offer "water based PU" coatings that they assure me do not decay like the old PUs did. No one wants that awful old stinky stuff."

It has been awhile since I received samples of the water based PU from a vendor, but it
took only one trip through the washing machine to have it start peeling. It was lauded
as being environmentally friendly. But I would like to see some if there are better
versions.

I do tent repairs. I find lots of urethanes don't last more than a few years. I haven't found a good way to recoat them.

I don't see the silicone coated ones peeling and if there is wear (they are usually pretty thin to start with, and abrasion can produce pin holes and furry spots) they can be re-coated using a technique one of the members here has posted.

> coatings on fabrics - even on very thin fabrics - are very different from a recycling
> point of view than impregnations.
However, I have found that the surface coatings delaminate - even some of the good ones. Yes, I have had the PU film tear off the surface of the fabric, many times. Not good: wasteful.

I have made tents from coated and impregnated fabrics. I will now only use impregnated fabrics. Apart from the delamination problem, I found that a coated fabric could absorb water on the uncoated side and then freeze. The resulting frozen tent was not only very hard to pack up, but there was a serious risk of damage to the fabric when it was folded up, from the ice layer. That's not acceptable any more.

> only silicone currently is impregnated into fabrics.
I doubt this somewhat. I have fabrics which have a siloxane-based coating on one side and a PU-based coating on the other side - and both seem to be impregnated into the fibres. Yes, examination with a microscope, and while under pressure.

More to the point though: I don't think many coating plants use a single polymer any more. They seem to be using blends of polymers to get their desired performance. But this is an area of black magic and trade secrets. Concrete data is hard to get.

> any non-recyclable product is backward in just that way despite whatever else it may
> have going for it. It's non-optimal
Rather a lot of idealogy here - too much for me. I contribute quite a bit to conservation organisations each month, but I think this is massively distorting what we really need to achieve in global conservation. The use of the most functional fabric and coating does not seem to me to be wrong if it works well and lasts well. Sorry, but we will have to diverge here. To each his own.

Cheers

Pulled off the Patagonia web site today:

"There’s a reason that ‘recycling’ comes last in the mantra: Reduce, Repair, Reuse, Recycle.
Recycling is what we do when we're out of options to avoid, repair, or reuse the product first. That's why I am so impressed with Patagonia for starting its Common Threads Initiative with the real solution: Reduce. Don't buy what we don't need. Repair: Fix stuff that still has life in it. Reuse: Share. Then, only when you've exhausted those options, recycle."
– Annie Leonard, author of The Story of Stuff

I completely agree with her. Recycling is just one step up from landfilling.

Do I need a new tent? oops... probably not. But if I get a new tent- isn't longevity and total mass of material important? If 1.1 osy basis weight silnylon is as strong as 1.9 osy basis weight PU nylon, then the silnylon uses a lot less raw material. If it lasts a long time that's good too.

Tents don't get tossed because they're no longer usable. They get scrapped because we're bored or there's something newer and lighter that sparks our interest.

It maybe true that silicone coated tents aren't as recyclable as polyester. I don't know. But recycling programs don't kick in unless there is enough volume to support it. Given the relatively small volume of silnylon in the market relative to polyester, it's probable that their simply isn't a large enough supply to warrant applying the resources necessary to figure out how.

So the question is do you simply abandon a fabric because it's failed to reach a certain threshold. Or do you expand the market in hopes that someone will find a use.

People have pointed out that there are a number of other technical issues with silnylon, ie. seam taping, stretching, etc. Again, are there real technical issues that prevent these issues from being solved or is it again simply a lack of volume.

With polyester fabrics priced at a small fraction of the price of silnylon, there is little incentive for large volume fabric consumers to make the switch. Until they start doing so the price of silnylon will probably remain high and any incentive to resolve any issues or recycle it small.

Ron

There are also siliconised polyester fabrics. I agree with the person/s that said amount of material for tents may not constitute a large (or significant) market for recyclable material.

More likely, a tent that lasts a while (and that people don't feel the need to "upgrade") will be better environmentally.

As for poly versus nylon. There are quality manufacturers that use both. I assume both are suitable. Each material has its benefits/drawbacks. I do suspect silnylon is overhyped these days (for some of the reasons others have mentioned).

I own a siliconised polyester tent and a silnylon. I am very happy with the polyester (I am also happy with one of the 2 siliconised nylon tents I have).

Re uv damage: I have had nylon become like paper (rips between your fingers). This does not trake long. Does anyone know the expected life of a tent at Everest base Camp? I suspect it's in the weeks or a month or 2 before it is damaged beyond use by UV.

On a different note... my desire for BPL to wind machine test shelters rather than rely solely on field testing where you can't account for all the variables (and can't even guarantee conditions will allow for a meaningful test - there may be no wind at all)...

If you look at the videos/measurements on Outdoor Magazin site there is often 5 or 10 km/h between a tent being stable and not (including catastrophic failure). I don't think only testing in a natural wind corridor is therefore an equitable way to test. You need to have tight control over wind velocity amount of turbelence and angle to the wind for a fair comparison between tents. You cannot infer a tents failure point unless testing it to failure (stable to unstable is such a small difference in wind speed often; you can also not infer a tents stability based on design it would appear -- there are marked differences on Outdoor Magazin of tents with similar designs that you would expect would fail at similar wind speeds).

I hope BPL is able to meaningfully control for some of the variables if unable to get a wind machine and does not jump to conclusions like "This shelter performed flawlessly in 80km/h and I'm "sure" it would take 100 km/h wind". Please stick to what is measurable.

Edited by stu_m on 02/10/2012 18:32:14 MST.

Sad but true.
Gear is most often bought for the kick of it. Not to mention that the majority of it is used, say five times a year.

On the lifetime of tents and fabrics. Yes there is a difference between ten and 20 years of service. That 100% increase is very good indeed. If one wouldn't put it in perspective to the natural resources used. The raw materials existed for thousands of years, was in use for 20 and then burned. Seen that way, I agree with Mike, we have no other option but to recycle. It's our obligation.

Stuart,

You said, "Does anyone know the expected life of a tent at Everest base Camp? I suspect it's in the weeks or a month or 2 before it is damaged beyond use by UV."

The average nylon fly’s useful life at sea level, during full sun days, is 21. There are two base camps on Everest and the higher one is 5,545 meters (18,192 ft.). With every 1000 meters increase in altitude, UV levels increase by 10% to 12%. So, 5,545/1000 * 11% * 21days = 12.8 days, rounded to 13. This passes the real world experience test as is attested to by Bob Gross in his post at http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=38299 assuming his tent had some use prior to leaving it on a summit for nine days.

He said, “While doing a mountain expedition, my team left one of my large dome tents erected at base camp. We came back after it about nine days later, and it was "brittle" from the sun exposure. I won't state that the fabric was totally ruined, but I never wanted to use it again.”

If the fly was polyester it would last approximately 61% longer in each of the above scenarios.

The above calculations are worst case scenarios and the time could be lengthened by the following known variables, plus possibly others: sun height, latitude, cloud cover, altitude, ozone, ground reflection, and fly color.

Edited by richard295 on 02/15/2012 11:35:41 MST.

Richard, how much would aluminized coating help to increasing the life of nylon fly?

"The average nylon fly’s useful life at sea level, during full sun days, is 21."

That's good news for those of us who make tents, right?

However most backpackers don't leave tents up during the day. I get reorders for shelters
after 7 to 10 years when the organization is using them daily during the summer months.

That ends up being 600 to 1200 days before the fabric deteriorates. (Most common fabric used in these shelters is 70d PU coated). I also had a scrap piece of 200d PU covering
my woodpile for 3 full years at 6000 ft elevation that was still waterproof and held
together. It was dark green.

21 days- well then, glad that's settled.

Huzefa, It should help dramatically.

David,

The following is a nylon fly useable-life deterioration graph for two flies. The first one appears to be close to what you tested; 70d PU coated Olive Drab (OD) nylon; this is the standard for small tents deployed by the US armed services. The second is a 30 denier yellow fly of the type that would be commonly used by an UL backpacker. It was a 1.1-oz (37g m2) nylon rip-stop fabric dyed with a shade (3) of yellow.

Edited by richard295 on 02/21/2012 17:31:22 MST.

Do we know how cuben fares with UV? Assuming the common 0.74oz variety.

Edited by dandydan on 02/21/2012 12:18:41 MST.

Hi Richard

That is consistent with my experience. Yellow nylon went like paper afetr a couple of years of heavy use, while the (same fabric) blue was unaffected. I think it has to do with the dye used.

cheers