RSBTR .93 Membrane Silpoly as a floor material

[Monte Masterson]

I’m aware that RSBTR and Dutch offer 20d silpolies with 4000 and 5300 HH’s respectfully, but I want something lighter for an inner I plan on making. I see that some of the 15d Membrane colors are rated at 2000 HH. Would it be waterproof enough for light usage? Thanks.

[Roger Caffin]

2000 mm HH would be adequate – when it is new. More would be nice.

We know that the HH does degrade in time.
You would have to be prepared to accept that the life of the fabric might be lower, although you can (perhaps) add more silicone coating in a few years time. I have done that myself.

Cheers

[Adam Kilpatrick]

The HH of silnylons of some cottage manufacturers in the past has rarely been above 1300mm. In 2010-2011 my friend and I used a solo tent each that misted in heavy storms (both of them did) as the HH wasn’t quite high enough, so likely below 1300mm HH (they were brand new with only a few nights on them when we had the first decent storm). Identical floor fabric to the fly. We did about 200 nights in them with no issues with the floor, we were cycle touring. I think you would have to do a LOT of nights on the 2000HH 15d floor before you hit any real issues. One thing you could do is occasionally use a partial groundsheet below it, eg a piece of light polycryo. It wouldn’t need to extend over the full floor area; just enough to cover the main brunt areas of where you put the most pressure and wear down. Eg if you are doing some desert walking, dry rocky ground, more potential for punctures, etc.

The other factor is if its a MYOG item, I can’t see you having many issues in a few years replacing it yourself in a couple of hours with another piece, if you think its starting to wear.

[Eric Blanche]

I have used the material to make a myog shaped tarp and I do not recommend membrane silpoly as a floor.  Maybe with a groundsheet it would be feasible.

 

But, as Adam says, it would be easy enough to replace it with another myog option…hopefully when this weight material becomes “strong” enough for floor use.

[Sam Farrington]

I’ve a different take on the RBTR “membrane” materials, resulting from the following experiences:
First, have tried using a coated membrane for scale models of tent designs, after using nylon of similar weight with no problems. Among other things, the models were meant to simulate pressures on the fabric.

Fine pins were used to hold the membrane in place. After a day or two, the fabric had come apart at each of the two pins located at the two peaks of the tent model (Think of the two peaks on a Tarptent Notch). Shortly after that, the fabric tore from the peaks partway down the canopies of the model. The pressure on the fabric before the tears was just strong enough to hold it taut. You can’t have much more pressure with pins over a music wire frame on a foam board; otherwise the pins on the board will just pop out. It became clear to me that a couple of tiny pin holes completely disabled the membrane fabric.

Second, looked at the FAQ section on the RBTR website, and found a chart rating the membrane very low in tear resistance compared to other fabrics. Don’t know if that chart is still up, but thought that at least they were honest about the fabric’s shortcomings.

So if you’ve settled on such a light fabric for a floor, you might consider the ~0.7 Sil/PU coated nylon from Rockywoods. You could put the sil side, which resists punctures, on the underside of the floor, and put the PU side on the inside, thus avoiding a slippery floor. Richard Nisley’s test results for the Rockywoods fabric are at: https://backpackinglight.com/forums/topic/108230/

Water pressure resistance (HH) is by no means the sole criterion for evaluating fabric for a floor. Abrasion, puncture and tear resistance must also be taken into account. The membrane is a polyester fabric. Sure, polyesters can do a fine job in garments, like jackets. But this is about a gossamer weight fabric. Without solid evidence that membrane beats other polyesters as well as nylons, would not expect it to have much abrasion and puncture resistance, which would be a disaster for a tent floor.

As it happens, after deciding on a couple approx. 1 oz. nylon fabrics for a tent outer, also looked for the lightest possible fabric for a floor. One of those outer fabrics has an HH over 5000mm, even after simulated aging using machine washings. But it is very slippery, way more than conventional silnylon. The other outer fabric is coated PU on one side, sil on the other, but a lower HH, around 2500-3000mm HH.  It is from a Sea-to-Summit Escapist tarp, so was dear.

Would go with the latter for a floor, except that I know that Duport’s 6,6 nylon is much better quality than most other nylons, and is used for cloth for hot air balloons. RBTR calls its 6,6 nylons “mountain” nylons, and the high HH one (>3000mm) weighs around 1.3 oz/sq/yd, compared with .9 oz you mentioned for the membrane, and 1.24 oz/sq/yd for the ‘common’ nylon. Only problem is, the 6.6 nylon has come only in white for quite a while now, even though the website says “other colors coming soon.” But there are darker shades of 6,6 at Thru-Hiker, and have some of the darker ‘mountain’ ordered earlier from RBTR.  Ideally a floor would be medium gray or khaki, to hide the dirt but prevent small items from getting lost, but you can’t have it all.

Comparing the ‘common’ and ‘mountain’ nylons from RBTR, a difference of .06 oz/sq/yd for a floor does not amount to much, only 0.22 oz for a 3′ wide bathtub floor for a solo tent, and not much more for a 4′ wide floor for a 2 person tent. Not being keen on a choice of black or white for a floor, will wait a bit to see if RBTR’s 6.6 color choices will be “coming soon.”

Don’t think a groundsheet would be needed for the “mountain,” and that would far outweigh its small weight penalty. Since the fly on my design does not include the vestibules, which are coated, and is therefore easy to replace, might try a fly made of Rockywoods’ 0.7 oz coated nylon and give it a whirl. But am reluctant to use it for the weight bearing fabrics.

Those are my conclusions, seeking adequate strength for lightest possible weight. Yours may differ.

[Roger Caffin]

@Sam

Fine pins were used to hold the membrane in place. After a day or two, the fabric had come apart at each of the two pins located at the two peaks of the tent model (Think of the two peaks on a Tarptent Notch). Shortly after that, the fabric tore from the peaks partway down the canopies of the model. The pressure on the fabric before the tears was just strong enough to hold it taut.

PHOTOS, must have photos!
Please?

Cheers

[Monte Masterson]

I’ve also been considering the .77 MTN Silnylon 6.6 from RSBTR. It is silicone coated on both sides instead of Sil/PU like the Rockywoods. I want the net tent for an SUL setup I have in mind. I’ll marry it up with a 7d trapezoid tarp I made recently (9′ X 6′ X 5′). The noseeum sides will be the 0.5 RSBTR with a 6′ foot D shaped #3 front entry zipper. Front and rear triangles .67 noseeum for better durability. 4 inch .292 carbon corner struts. I figure it would come in around 6.5 oz maximum.

https://ripstopbytheroll.com/products/0-77-oz-mtn-silnylon-6-6?variant=28828264202288

 

 

 

[Sam Farrington]

Roger, re: “PHOTOS, must have photos!”
Alas, those models were taken down and the fabric and music wire pieces thrown out.

Monte and John, the RBTR .77osy sil is even more slippery than the ExText 20D, probably because the RBTR is the lightest gossamer weight. Can’t think of anything that would more bunch up and let a mat slide around. It would be just as bad with a ground sheet that would allow it to slip even more. It is so bad, I would not use it and plan to throw it out. The Rockywoods stuff at least has a PU coat on one side that gives it some body, and has been tested by Richard, an independent source. Believe it or not, there was a thread about using it a floor.

P.S. Oops, wait a minute – maybe a cover strung over a hammock for the RBTR .77osy.

[J-L]

I’d pick their 7D MTN Silnylon over the Membrane Silpoly for a floor. I was impressed with my sample – it seemed harder to tear than Membrane Silpolys I had previously handled.

This guy used the 7D Rockywoods silnylon for a floor, so it’s at least possible for awhile:

https://backpackinglight.com/forums/topic/7d-silpu-bathtub-groundsheet/

If you are pairing it with a groundsheet, I think very light floor fabrics make sense. If you are not using a groundsheet, I think the 1-2 oz penalty of a 20D-30D fabric is worth the substantial increase in durability.

[Adam Kilpatrick]

NM-posted to wrong thread oops!

[Sam Farrington]

Hi Roger,
Finally found an old photo of the tent model with Epic fabric stretched over a wire frame. Since I lost my picassa program courtesy of windows support, have had to relearn photo editing without it, but finally was able to resize it to fit BPL forums:

You should be able to make out the pins at the peaks of the model.  Forgot that I used a cork bulletin board from Staples, not foam board now used for smaller models.  The cork board holds the pins much better when working with fabric.  When RBTR membrane was used, the tears occurred as described in my earlier post.  The tent shape has since been resized to increase the curvature of the poles to add internal space.  Photos of that have been posted on other threads, but will put one here for your convenience (this model is 8″ long, by 3″ wide by 4″ high, and the scale is 1″ = 1′, not including the vestibules – the doll is 6′ long).  So the outside dimensions of the solo tent will be 8′ long, by 3′ wide, by 4′ high, very spacious compared to currently marketed tents, but close to the dimensions the Eureka! used for solo domes at one time :

Hope all is well.

 

[Roger Caffin]

Hi Sam

Interesting, and thank you.

When you say ‘tear’, do you mean a rip, like a scissor cut, or do you mean the warp and weft came apart, were dragged apart? Very curious.

Cheers

[Sam Farrington]

Roger,
I mean either the warp or weft, leading from the pin hole downward, came apart.
Poor choice of words. Thank you.

Note: That, and the RBTR membrane is also woven of polyester threads, so will not endure as well as the nylon in the Rockywoods 7D. Also, I moistened the RW 7D on each side, but could not get it to stick to itself like saran wrap, as suggested in a post in the thread linked by John. The water on either side just beaded off as happens with good DWR. Maybe longer exposure to moisture would create the sticking, so will test for that also. Attaching a sticky fly would be a PITA. Don’t even like attaching saran wrap to cover a bowl. Please note, unlike the OP, I’m intending to use the RW 7D for a partial outer tent fly, not a floor. If it proves to lack durability, will use a higher denier, maybe the Extrem Textil 20D, which is only a third of an ounce/sq/yd or so heavier; but will see what is available when I get to that point. Maybe even the DCF which from all accounts is much better than the Cuben. A fly would be a good project to learn more about taping. But am not at all keen about the lack of elasticity in DCF. Noise, less durability, and higher folded volume, to name a few concerns.

[Roger Caffin]

Right, understood. Distortion of the weave is common to many light-weight fabrics. I have the same problem with very light silk fabrics I have used to make liners etc.

My objections to DCF are similar to yours: no elasticity for absorbing shocks or small errors in sewing, and when it has been stuffed into a sack a few times it tends to develop pin holes at the creases.

Cheers

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