Strength of .93 oz Membrane Silpoly vs 1.24 oz Silnylon

[Mario Caceres]

James has very good points.   Looking at the specs of Rockywood 0.7oz silnylon its has a PU coating in one side and sil on the other side, where RBTR 0.93oz silpoly membrane is coated with sil on both sides.  My understanding is that taking the same base fabric and coating it with sil in both sides is stronger than the hybrid coating.

Rockywood lists the tear strenght of their 0.7oz silnylon at 1.2 lb in warp and 2.5 lb in weff, but that seems way too low.  I’m surprised RBTR does not test and post the tear strength of their offering.  The test seems pretty easy to make without any sophisticated equipment.   I think having actual numbers would be extremely useful for folks when deciding which fabric to use for their different projects.

[R]

I found Rockywoods 0.7 to be good for ~15 lb/in.

https://backpackinglight.com/forums/topic/108230/#post-3370891

I’ve always taken tear strength and tensile strength to be two different things.  Can some one with some expertise comment?

[Aaron Sorensen]

• Seams to me as all this backing fabric for strengthening could be made easier?

I would just roll the edges over 1 1/2″ sew it, then roll it over again covering the exposed edge and sew again.

That would give you 4 layers of fabric to sew your tie outs on.

just sew the tie out only on the 3/4″ edge.

[Sam Farrington]

Looked at this thread again much later, and after running into some concerns with the the RBTR membrane fabrics. In testing tent designs using scale models, discovered that pinholes in the membrane fabric had a tendency to spread into runs that followed the warp or weft (grain). This was without any undue pressure on the fabric, as would be the case with a tent canopy in a storm. This has never occurred with any nylon fabric models. Since pinholes can eventually occur with a tent, do not want them running and creating a long tear, and therefore will stick with ripstop, or at least mini ripstop, for the next tent.
Right now that looks like the Rockywoods 7D sil/PU coated mini-ripstop nylon, for a main canopy at least; and a slightly heavier ripstop nylon from a StoS Escapist tarp weighing about 1.06 osy for the vestibules or end covers that get rougher treatment. Would have liked to use polyester for the end covers to avoid sag, but don’t think membrane is the answer.
Will say that the RBTR chart by Justin Oliveri is straightforward about the low puncture and tear resistance of the Membrane fabric.

[Ben L]

Sam,

That’s some interesting data, don’t suppose you could put some pictures?  I assume this is the standard membrane fabric, and not the PU4000 version? I’m considering between the various RBTR fabrics and waiting on a sample pack at the minute. This is just the sort of info I need.

Thanks,

Ben

[Hoosier T]

 In testing tent designs using scale models, discovered that pinholes in the membrane fabric had a tendency to spread into runs that followed the warp or weft (grain).

This was established in this thread already. The solution is to use glued reinforcements. No stitch holes to tear…I’ve had three different Membrane tarps and after the initial issue with sewn patches, I have had zero issues once moving to bonded patches. I’m afraid that your inconclusive findings will unnecessarily drive people away from a perfectly good material that works when built properly.

 

[Sam Farrington]

T Hoosier:
Perhaps you thought I was referring to needle holes from a machine but was not. Was using just a few very fine pins to hold fabric taut to a scale model tent frame made of music wire. Was surprised to see the fabric open and spread around the hole to a tear following the grain, since had never observed anything like this using nylon, even Rockywoods 7D, which is a much lighter material, but nylon.

There were no findings, just an expression of a personal preference based on what was observed. Many of us are without well equipped laboratories to present scientific findings. However, that should not deter us from expressing preferences based upon experiences and the reasons therefor.

Please note that pinholes can occur in any part of a tent surface for a variety of reasons reported here from time to time. One cannot reinforce the whole canopy. And yes, I do not think that sub one ounce polyester fabrics are a good material for tent canopies, especially when there is not any ripstop, mini or larger, in the weave. I think this is a fair conclusion from what I observed. Since you do not, we will just have to disagree on that point. I hope we can do that in a friendly and constructive way.

[James Marco]

7D and 10D nylon fabrics are on a par with the older spinnaker cloth. They both need some sort of ripstop to handle any tendency to tear. Without a gridded ripstop, they can just continue to run. The micro-ripstop seems OK, but this still can tear.

I personnaly do not believe that current tent fabrics are up to the task of a ten year tent without ripstop or without a relatively high weight penalty. Anyway, I understand about ripsop failures where the thin threads overlap the heavier ripstop threads, thus forcing them to take accelerated abrasion. The solution is to use micro ripstop in selected ways. For example, the low HH means it is not suitable for flooring; low strength means it is not suitable for high wind resistant shelters. To use 10D micro-ripstop fabric for a pack is asking for trouble.

So, it is not so much a fabric issue, it is a matter of shelter design. SilPoly or Membrane is suited to small solo shelters, preferably, <3’high to reduce wind loading and more circular designs increase supported strength/reduce wind loading. 10D SilNylon is suited to somewhat larger shelters, <3.5’high with larger flat panels between supports (a typical diamond type shelter.) 1.2oz Silnylon can be used for up to 4′ high shelters with up to 9′ panels between supports (a typical ‘A’-frame shelter or short 3.6″ lean-to shelter.) Heavier fabrics and different designs will impact this somewhat. For example: a 2 person tunnel tent made with 10D nylon will *just* fall in these general specs. A 10D pyramid will likely fail, though.

As you can see, strength per weight becomes important. To low, and you get a fragile shelter good for below tree line, in a sheltered location. To high and you are carrying excess weight. It does no good to carry a 10pound bomber for solo summer conditions in the north-east…wasted effort. But, you always need some margin for those exceptional trips of stormy, windy, rainy, snowy weather. And, to give your shelter some long term (10 year) durability. You do NOT want to fight with your shelter all night and hike all day.

All things become important. Stitching, thread, hemming, seams, panel strength, supports, staking, reinforcements, fabric, loops, etc… As well as the conditions (worst case) you expect to encounter. (I have taken my shelters through tornado weather, I understand what worst case means…NOT the exceptionally bad case…) As always, the least weight that will do the job is the correct choice. In every case, however, I see little use for poly membranes. Nylon is always a stronger choice for the weight.

[Monte Masterson]

” Nylon is always the stronger choice for the weight”

I 100% agree. I’m not a materials scientist, but every bit of information I’ve been able to uncover basically says that nylon is stronger than polyester. And with superlight materials it becomes all the more important.  I’m sure the 4000 mm silpoly works good for floors though.

I’ve said it many times on this site.  I think the 0.7 Rockywoods  is the way to go when it comes to the lightest (non DCF) materials. The Rockywoods costs nearly double that of the light silpolys, but worth extra expense IMO. I’m amazed at how strong the stuff is for its weight

[Jerry Adams]

The advantage of poly is it doesn’t stretch after you set it up

Sometimes, with nylon, I’ll wake up in morning and it will be very loose, in my face

With poly, you just set it up, tighten, and you don’t have to go back and retighten

Supposedly, poly absorbs less water.  I made a mid with poly and have used it a number of times including 30 MPH wind.  So far so good.  I’m waiting for a trip where I pack it up wet and bring it home so I can get wet weight and compare to dry weight.  I’ve had it out in the rain but was dry on the last day so it mostly dried out.

I will now check carefully for any pin holes, thanks for the warning.

I am comfortable with the apparent contradiction of one person getting pinholes, not acceptable, another person not.  In general I don’t like grid stop for the reasons James gave.  I’ll have better experience in a year of use.

[James Marco]

Yeah, Silnylon does react to weather, whereas poly does not. Anyway, as an overview that was my thoughts. There are ways around nylon stretching, just as there are ways around pinholes and other deformations with poly. Weight-wise, these are about tit for tat, so I ignore them.

I personally use tight hair ties for setting up dry. Much of the sag gets taken up by any bounce back. But, they are a gram or two heavier than plain guylines…again, all loop to loop connectors. They can hold up to about 20pounds each, though I have been known to double them on the windward side. I carry a half dozen or so looped together on my pack. If it adds up to an ounce I would be surprised…usually less but they vary a lot. Anyway, I have also been known to drop a 5 pound stone on my tarp corners, this also manages tension and I don’t need to carry it. It doesn’t do much for the tarp, but I don’t worry about that. Generally, nylon is fairly resistant to abrasion and I don’t sleep under the corners. Wind is often pretty bad in the ADK’s, some of the hills get some of the worst winds on the planet. Mt Washington is only around 50 miles off with its damn near 200mph winds…I have seen 60-70 while out.

Anyway, I believe that surface tension has a lot to do with water weight. If something is wet, you can shake it, but it will remain wet. Likely less with poly, but still a large fraction of the total weight. Unless you spend an hour or so wiping it down, you will always carry that weight. I could be 2mi down the trail in an hour…

[Taylor_At_DP]

From a materials standpoint nylon soaks up A LOT of water compared to polyester. It grows while doing so and the modulus drops. Polyester picks up less water, is more stable and is lower stretch(higher modulus).

Wet tent performance might be interesting to look at when comparing the performance vs weight.

Cheers,

Taylor

[Monte Masterson]

I can appreciate the fact that silpoly has less sag/stretch and retains less water than silnylon, but the big question for me is: which material of equal weight is stronger in high winds, both in a dry and wet state?

I am willing to deal with the negatives of silnylon if it doesn’t shred apart in a major blow, when a comparable silpoly would fail under the same conditions.

[James Marco]

Taylor, yes. But most tents are made with nylons also have a silicone coating. This improves the water resistance a lot. Normally, Nylon6,6 has about a 10-15% strength reduction when saturated with water. But the research into this area usually indicate that this is only achieved when the raw nylon is immersed in water for 24 hours or more. (Normally I have experienced numbers far less than 10% since rain storms never penetrate to me.) In any case, this puts it on a par with poly or better than poly when coated which silpoly would derive no benefit from. So, “equivalent or better” even when wet is how I read that stuff. This is not counting ROBIC nylon which is an unknown…I could not find any wet data on it in an hour of searching. But, I suspect it will perform slightly better than Nylon6,6. I just do not find anything documented. But even if it *is* the same, a basic ~50% strength increase means a 10% decrease when wet still leaves it stronger. (It is touted in several posts at Ripstopbytheroll as having a lot *less* stretch, but that is anecdotal…) It also weighs about 1oz/yd, not the original 1.24oz/yd though it is unclear on how it is weighed…it might very well be the same stuff.

[Adam Kilpatrick]

Those who’ve handled them; thoughts on using the 0.93oz Membrane Silpoly, or, the 7D rockywoods for ponchos?

[James Marco]

The 7D fabrics are normally quite slick, perhaps more so than 1.2oz silnylon. It is a bit looser/thinner, generally, but rather noisy. My jacket made from this reminds me of a plastic bag, sometimes…not that loud but near my face. Some use will alleviate the problem, though. It is generally a good light duty fabric, but gets holes due to embers/sparks near the fire relatively easily. (I was putting on a couple logs one time and over heated the cuffs. The fabric got stiff and actually broke the next day requiring some duct tape to patch it…still holding after 3 years.) The fabric holds up well, but it is not all that water resistant The PU coated stuff I have not worked with yet, just the plane-jane 7D on the jacket. The new stuff is touted as ~1500mm but I do not believe it will hold that number long. Personally, I would recoat it after the first or second use develops some stretching. First generation stuff was not coated, more like spinnaker. The micro-grid is nice. A drop of super glue where I snagged it and pulled a couple needle holes open. Pressure points will undoubtedly start leaking in a few uses at this low number. Straps, belts, shoulders and your head would likely end up the culprits, I believe. Over your pack will work better, but can build up small puddles. I always wear a hat under a poncho, soo, my head is not normally a problem. (I also make sure my “dry” gear is in “dry” bags.) It should work fine as a poncho, and likely weigh around 4-5oz after recoating…likely 3-4oz before. A combination poncho/shelter will weigh a couple ounces more: heavier seaming, loops and pole reinforcement patches. Oh yeah, use a rather fine needle (around a 7 ball point and a thin poly thread. I don’t care for ponchos though and went with a fully waterproof rain jacket. Ponchos snag easily on scrub and make rock hopping/blowdown crossings more painful than needed. You cannot see your feet sometimes. They never protected me from wet pants & shoes. HYOH.

While surface durability is a problem, especially with dual coatings(DWR on one side, PU on the other) on thin fabrics, you can retreat this with a 20:1 mixture of mineral spirits and silicone caulk on the outside, DWR side. It isn’t expensive and it only takes a couple hours. Setting up, and brushing it evenly/thoroughly are the problem. An airless sprayer works OK but the mix needs to be worked into the fabric with a brush for best results. DO NOT apply heavily. Some do, but it can peel if you get the mix wrong. 20:1 by VOLUME. I just eyeball it leaning to thin so it could be 25:1. A little, around a half pint should be enough to do a poncho. IFF it will not form a sheet but rather puddles up like a windshield, it is too thin. A wider 2.5″ bristle chip brush works to work it in/spread it.

[Jerry Adams]

“which material of equal weight is stronger in high winds, both in a dry and wet state?”

Nylon is a little stronger than poly

If you don’t appreciate that poly stays taut and maybe is better when wet, then nylon is better

.93 is pretty light for clothing, more likely to snag or get hole in it.  The surface area of clothing is small so a little heavier fabric won’t weigh that much more.

When I’ve used generic 1.5 ounce silnylon from years ago, it seems like the fabric holds more water.  Takes longer to dry off.  This new silpoly shakes water off better and drys off faster.  The next time I use the tent in the rain and pack it up wet (after vigorously shaking off water) I’ll weigh it.

[Sam Farrington]

Ben,
The membrane fabric that I referred to in my post of March 27th was the RBTR membrane silpoly, 15D, PU4000. Test results for that fabric were posted by Richard Nisley on BPL on 10/13/16 using a sample I sent to him. Regret I did not keep the fabric pieces that developed runs, so cannot post pictures.

Jerry,
Re: “With poly, you just set it up, tighten, and you don’t have to go back and retighten.”
I’m not sure of the extent to which falling temperatures and moisture play in causing nylon to sag, but suspect that both may be involved. Have tested tent fabrics for sag using plastic embroidery loops, and found that temp drop, and either humidity rise or rain were all associated with nylon sagging. Some of the fabrics were coated on both sides with sil, PU, or a mix thereof, and were highly water resistant; so have doubts that water penetrating into the nylon fibers was implicated in the sagging. Have noticed that the newer fabrics coated with sil on one side and PU on the other showed less sagging, and so those are what I will now use for any nylon tent canopy or fly.

I’ve found that sagging of tent vestibules or end covers can be further reduced with shock cord loops around the tent pegs, and have noted that Roger Caffin has reported similar results. This photo of a One Planet Goondie (AU tent) which garnered some interesting responses on BPL, was taken in the early morning at the end stages of an all night rain storm, and shows the most sagging experienced with this tent that I’ve never had to retighten:

The outer green fabric is 15D nylon, and the shock cord front and rear loops keep the fabric adequately taut, although it does not become drum tight until the sun comes out for a while.  Don’t know the exact composition of the coating, but know that it is at least PU in part, and not pure silnylon.

Having found that nylon sagging can be adequately addressed, and assuming equal weight and high water resistance, I agree with Monte that the big question is which fabric will hold up better in high winds.  In other words, minimal sagging or wrinkling is not a deal breaker for me if the fabric will provide the best protection for its weight.  Intend to use the RW 7D for a fly that covers the occupied area of a tent, but not the end covers or vestibules.  Already know that the RW 7D has high water resistance and is protected by a micro riptstop weave; and If it does not soak up water and is reasonably durable, it will remain.  If not, it will be easily removable, and easily replaced by a slightly higher denier nylon.

[Roger Caffin]

sagging of tent vestibules or end covers can be further reduced with shock cord loops around the tent pegs,
Definitely. I would never be without those bungee cord loops at the lee end, but never at the windward end. NEVER.
One 150 mm long loop of 4 mm bungee cord at each lee corner, pulled out to about a 40-50% stretch.
Kowmung R Nov/2017
You can see the two corners in this photo, and the almost drum-tight nylon fabric. That tent must be at least 10 years old, and doing just fine, despite the tight pitching. If anything, I think the lack of slackness and flapping has made the fabric last longer.

Cheers

[Jerry Adams]

“I’m not sure of the extent to which falling temperatures and moisture play in causing nylon to sag, but suspect that both may be involved.”

same here, seems like it sags even when it doesn’t get wet

a problem with shock cords is if it’s windy they’ll stretch, the tent panel will blow around more

If you can stake it so the edge of the tent is touching the ground with a big rock on it so the edge won’t move, a little better in wind

[Roger Caffin]

a problem with shock cords is if it’s windy they’ll stretch, the tent panel will blow around more
He He He
When two loops of good 4 mm bungee cord are given a 50% stretch as in the photo above, the tent does not flap! But note that the windward end uses short loops of 3 mm nylon cord: they do not stretch at all.

Rocks on the edge of the tent – well, that can be a good way of abrading a hole through the fabric. Lots of snow & ice – no problem.

My experience.
Cheers

[Jerry Adams]

I use 1/2 inch nylon webbing, that stretches a lot less than 4 mm bungee.  And it flaps.  The tent is what’s stretching.

I have a floorless mid rather than a tunnel which behaves a little differently.

Put rock on webbing, not on tent.  That won’t abrade.  You want the webbing fixed to the ground as close to the tent as possible without abrading the tent.

 

[Roger Caffin]

Hi Jerry

Perhaps I did not explain myself well enough. The bungee cord puts the whole tent under tension, so that if the nylon stretches a little the tent is still under significant tension.

Yes, a floorless mid will behave a bit differently – exactly how I am not sure. With a tunnel, the tension in the roof pushes the poles down onto the ground – quite hard. I don’t think the groundsheet plays a significant role here, not at least in lengthwise tension.

Webbing for rocks – sounds good to me.

Cheers

[Jerry Adams]

many good techniques here : )

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