Her måtte jeg faktisk undersøke litt rundt hva jeg selv mente å huske, for å gi et bedre og mer konkret svar. Så jeg kontakt Robens, samt undersøkte litt ellers.
PU er ikke bare PU. Det kan være PolyESTER Urethane, eller PolyETHER Urethane.
Sistnevnte er det som er gode greier, ofte forkortet til både PU, PE, og PUE. Robens, blandt andre, bruker PolyETHER på innsiden, se bilde:
I tillegg for å lese mer om silpoly vs silnylon, anbefaler jeg STERKT å lese hva Dan Durston sine egne tanker, tester og dypdykk sier rundt bruken av denne, blandt annet da på polyester duk, siden hans "ikke pro" versjoner bruker dette.
Litt sitater:
"The traditional way of coating tent fabrics is with a PU (polyester urethane) coating, which is highly problematic stuff. It substantially weakens the material and slowly breaks down from water (seriously). Worse, it absorbs water inside so it feels dry when it’s not (much like nylon). Then you store your tent thinking it’s dry while both the nylon and PU are hiding moisture inside, and then when you pull it out 6 months later you find the coatings have broken down and are delaminating.
A much better coating is silicone. It’s solidly waterproof (when applied heavily enough) while actually strengthening the fabric instead of weakening it, plus being largely immune to degradation. It’s way better than traditional PU but still has a couple of downsides: you can’t seam tape it, and it’s so slick that tent floors become awkwardly slippery if you’re camped on any sort of a slope.
....
More recently, a new formulation of PU has come along called polyether (vs. ester) urethane that doesn’t add as much strength as silicone but doesn’t lose as much as traditional PU either, and it solves both the degradation issues of conventional PU and the downsides of silicone (slippery, can’t seam tape). Confusingly, this coating is still called PU but is also called PE and PEU. It’s hands-down better than older PU, which is why mainstream companies are making the switch. About 80% of premium mainstream tents are now switching, and older PU formulations are becoming obsolete on premium tents.
With the X-Mid, we use dual coatings where the primary coating is a heavy coat of silicone on the outside for high waterproofness and additional strength. Then we also apply a thinner coat of PEU on the inside to add even more waterproofness and so we seam tape it for you while giving a non-slippery floor. Some companies will tell you that using only silicone is stronger yet and theoretically it is, but the critical point here is that we are using a similar amount of silicone as most silpoly but then we also add a second lighter coat of PEU that has little effect on strength. Yes, it would be even stronger yet (slightly) if that second coat was sil too, but the difference is slight and PE brings several advantages (seam taping, non-slip floors). Compared to single coated silpoly, we are paying more for the additional inner PEU coating, so we can then spend more for seam taping because that gives you a better product that is ready to go, whereas user seam sealing is a hassle and doesn’t work as well."
Det var et lite utdrag, synes slikt til tider kan være litt fascinerende.
Ergo: ikke avvis PU basert på gammel PU. Silikon på utsiden og PU(PE, PUE) på innsiden har betydelige fordeler, uten at det ofrer så mye som man tror. Mye ord blir slengt rundt i diskusjonen om silnylon vs silpoly- og det er mange variabler så absolutt, men det er verdt å undersøke, når ikke alt er så relevant som man skulle tro. 😅