The materials used in your outdoor equipment are crucially important and yet reliable information is hard to come by. That occurs due to a scarcity of good info on materials science and persistent myths in the outdoors community, but mostly because gear companies all want you to think their materials are flawless and better than everyone else’s, and thus vague descriptions are supplied (e.g. “very waterproof and durable) while advantages get exaggerated and weaknesses are omitted.
Particularly problematic is that some companies are willing to go to unfortunate lengths to convince you their materials are better, irrespective of the truth. That includes engaging in excessive marketing hype (e.g. referring to 10D fabrics as “bomber” when actually 10D fabrics are about as the least durable tent fabric there is), omitting crucial information that undermines their point (e.g. touting DCF as having a super waterproof 8000mm HH without telling you that it regularly forms microcracks and pinholes which make it typically the least waterproof material option), or outright false information.
X-Mid fabric under the microscope
The X-Mid tents have been a pioneer in the use of polyester in lightweight tents. Since they are perhaps the best known polyester tents, they’ve had to swim upstream against a lot of misinformation on the topic. Thankfully polyester is getting a lot more popular now and looks be taking over with companies like Black Diamond, Six Moon Designs, MEC, Yama, Lightheart Gear etc now making the switch. But it’s still worth taking the time to explain why polyester is so much better, to call out some wrong information, and explain the rest of the materials choices we use in the X-Mid. As you might expect, all the materials choices in the X-Mid are reasoned from first principles to deliver the highest all-around performance. That’s not to say there aren’t compromises though – the most durable fabric will never be the lightest.
20D Sil/PEU Polyester
The X-Mid uses a 20 denier polyester fabric for the fly and floor, which is sil/PEU coated. 20 denier (or 20D) refers to the thread weight, where lightweight tents range from 7-30D. At 20D, the X-Mid is a bit more durable than most lightweight tents from mainstream companies (e.g. Big Agnes, MSR) which are typically 10-15D, but it’s still a light fabric and needs to be treated responsibly. We think 20D fabric is a nice well rounded choice because it is a durable enough to use without a groundsheet if you use proper care (e.g. checking camp spots for sharp sticks and rocks). Lighter fabrics such as 10D commonly require a groundsheet and thus a 10D tents may appear lighter, but it ends up just as heavy and more complicated when you add the groundsheet.
Polyester vs Nylon
The most contentious fabric topics these days is polyester, or more specifically polyester vs nylon. There has been an unfortunate amount of misinformation about polyester with otherwise reputable tent companies making unfortunate statements about it, such as that it is much weaker than nylon or just a cheap fabric.
For example, Seek Outside writes:
…where their claims of nylon being “ounce for ounce tougher” and small packing while poly is “a lot cheaper” are all false.
Similarly, SlingFin writes that poly has a “very low” tear strength and dismisses it as being for wimpy tents, while brushing off key advantages such as UV resistance:
That’s disappointing to read that from a tent company who should know better. Seemingly they are repeating long standing myths instead of actually doing the research, as poly does not have a “very low” tear strength, nor is the vastly superior UV resistance of polyester a “belief” that is “assumed from dated curtain research“. The vastly better UV performance is a well established fact which is why, for example, the entire boating world uses poly.
The truth is that nylon comes in a variety of formulations, where the best possible nylon (“nylon 6,6”) is roughly equal in strength to modern polyester (there are new polyester formulations in the lab that are much stronger yet, but not commercially available). Instead of believing a tent company with a vested interest in promoting one type of fabric, we can look to DuPont who actually design and produce these fibers. In their documents here, they provide the strength of polyester vs. nylon 6,6 and give that latter a 1% advantage in ounce for ounce tensile strength (circled below):
A 1% advantage might sound like a slight edge and some other sources do give nylon 6,6 up to a 15% advantage, but in the field nylon is ounce for ounce inferior for two reasons. First, is that it is a “hydrophilic” (water loving) molecule, so when you camp in wet conditions it absorbs water and swells up. That makes it heavy (gaining 1 lbs in water pretty easily), slow to dry (since the water is in the fibers), and weaker by about 10% (since the swelling process stretches the molecular bonds). Most noticeably though, as the material expands by 2-4% it ends up with several inches of slack over the arch of the tent, which is why most tents look limp after rain with the fly stuck to the inner tent. All of those are pretty serious issues for a tent fabric. Even if nylon is a bit stronger for weight when dry, in stormy conditions where you need that performance it quickly gives up that advantage while potentially doubling its weight. Meaning that the next day you’re carrying a heavy shelter down the trail for no strength advantage. You can read more about those chemical properties here from a company that actually makes these fibers. What about poly? It is hydrophobic (hates water) and thus does none of that. In wet stormy conditions poly remains strong, light, fast drying, and retains a nice tight pitch. Outstanding qualities for a tent fabric.
The second big weakness of nylon is UV degradation. Nylon is highly susceptible to UV degradation, where even if you break camp early and set up late, your tent will degrade in strength over a few years. A new nylon tent can lose 10-20% strength in a weekend of pure sun, or in roughly a season of regular use if you take it down in the daytime. Hence why 5-10 year old nylon tents are commonly under 50% tear strength. Thus polyester has about the same strength when new but is far stronger in the long run. These two reasons combined are why any strength advantage of nylon is just theoretical and doesn’t play out in the field. Why then do some companies say nylon is far stronger, with some claims up to 100%? That’s because they are conflating differences between coatings (silicone vs PU vs PEU) with fibers. Silnylon will be stronger than a PU poly, but entirely because of the sil vs. PU difference and not the fibers (see below for discussion on coatings).
All of this discussion on strength ignores that there are many other aspects of fabric durability, such as abrasion resistance and puncture resistance. You don’t hear about these because no one thinks nylon has an advantage there. Abrasion resistance is very important for a tent floor – moreso than outright strength – and poly is at least equal to nylon here with most material science finding that polyester is more abrasion resistant for the weight.
The inescapable conclusion here is that nylon has almost nothing good about it – so why is it popular? After poly and nylon were invented in world war II most tents did use polyester. Then with the movement to lighter tents in the 80’s backpacking tents did switch to nylon but simply because only nylon was available in lighter versions (due to demand from other industries with more sway than the small tent industry). Meanwhile poly remained only available in heavy weight versions and thus relegated to use only in heavier mountaineering and car camping tents. In the last 5 years that has changed with 15-30D lightweight poly now commercially available. Thus, lightweight tents are switching to polyester with many brands making the switch each year.
Lastly, what about the claims that polyester is cheap? It would be great if the superior tent material was also lower cost, but unfortunately that is also misinformation just meant to make poly look bad. Lighter fabrics use smaller threads (e.g. 20D) so they are higher threadcount – which makes them more expensive to weave. Since historically only heavy/low threadcount poly was available, it was relatively affordable. Now that high threadcount poly is available, it costs about the same as high threadcount nylon. Browse the fabric selections at a fabric retailer like RipstopbytheRoll.com and you’ll see the prices are roughly the same. The companies that are telling people this are just repeating tired myths and probably haven’t seriously looked into it.
The traditional way of coating tent fabrics is with a PU (polyester urethane) coating, which is pretty terrible stuff. It weakens the fabric, and likes to absorb water which causes it to break down when stored like that, resulting in delamination, mildew etc. Even if you think you dried your tent, there is probably some moisture inside the material that can result in it going gummy or flaking and peeling eventually. Everyone who camped in the 80’s and 90’s has a tent failure story like this.
A much better coating is silicone. It’s also solidly waterproof (when applied heavily enough) while actually strengthening the fabric instead of weakening it, plus being largely immune to degradation other than physically being abraded away. It’s way better than traditional PU, but still has a couple 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 quite add as much strength as silicone, but still adds quite a bit while avoiding the degradation issues of traditional 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 rapidly making the switch. About 80% of premium mainstream tents now switching and older PU formulations becoming obsolete.
With the X-Mid we use dual coatings where the main coating is a heavy coat of silicone on the outside for high waterproofness and additional strength, and then we also apply a thinner coat of PEU on the inside so we can seam tape it for you and to make the floor non-slippery. Some companies will tell you that using only silicone is stronger yet and theoretically it is, but the key 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 adds even more strength, so the PEU makes it stronger than most silpoly. Yes it would even stronger yet (slightly) if that second coat was sil too but the difference is trivial (a few percent). Compared to normal silicone coated poly (“silpoly”), we are paying more for the additional inner PEU coating, so we can then pay more for seam taping because that gives you a better product that is ready to go, whereas user seam sealing is a hassle for you and doesn’t work as well.
When you see a company touting strength as a reason to use pure silicone over a dual coated silicone/PEU, almost certainly it’s a cover argument to hide that they are saving costs. Factory seam taping is expensive, as are dual coated fabrics, so they skip these costs and then they tell you they did it for strength reasons. You can tell this is happening because strength is almost entirely irrelevant for a floor (versus abrasion resistance) and yet those same companies are still using only silicone and no seam tape there. We seam tape because it makes for a better tent, even if that does mean added costs.
The other type of fear-mongering companies do to justify using pure silicone over silicone/PEU is they will bring up the outdated flaws of traditional PU (which is terrible due to degradation) to justify not using modern PU (aka PEU), even though these flaws don’t apply to the newer PU/PEU formulations. For example, here’s the founder/owner of a major tent company arguing against sil/PU by providing a scary sounding but obsolete argument:
To the lay person that sounds like a good argument, but once you know that mold, mildew and delamination are irrelevant for modern PU/PEU, it falls apart entirely. There is no reduction in lifespan. The #1 lifespan reducing thing that customers should be wary of are excessively lightweight zippers and UV susceptible nylon.
All of that ignores the most important coating related topic: is it waterproof? That’s way more important than splitting hairs on tear strength. The industry standard approach here is to provide an HH specification for the new fabric which basically tells you how much water you’d have to pile onto the fabric to get enough pressure to push it through. Unfortunately these new specifications are almost useless because it ignores degradation. Virtually all fabrics are waterproof enough when new but then degrade where a high initial HH might not translate to one down the road. DCF for example starts out very high (8,000mm) but quickly forms microcracks and pinholes under stress so it can quickly be at 500 mm. Similarly, Sil/PU and PEU coatings might also be very high, but if they are thin coatings or not well impregnated into the fabric they will wear down quickly. This is partly why traditional PU coatings were commonly rated at 10,000mm (they’re mostly external and easily degraded so they need to start that high to last okay). All coatings degrade a surprising amount, were the key is to keep them above ~600mm for as long as possible because real world leaking happens at about 600mm in heavy rain.
Below is a chart showing the hydrostatic head of the X-Mid’s fabric (green) as it is subjected to wear cycles, in comparison to 4 other fabrics from popular competitors. We haven’t cherry picked which competitors to include – rather we submitted our fabric to an independent lab for testing whom had recently tested these other fabrics on their own accorded, and provided the results to us for context. The blue and grey fabrics in particular are used in by two popular lightweight tent companies for almost their entire product lines.
You’ll notice all but one of these fabrics starts out at 3500mm – that isn’t the real maximum for these fabrics but just the upper limit of the testing equipment. The key takeaway from this chart is that the X-Mid fabric isn’t as high as some fabrics early on but because the coatings are deeply impregnated it holds that waterproofing for longer. By the end (16,200 wear cycles) it is the most waterproof fabric (Note: 16,200 wear cycles roughly corresponds to 3 months of continuous high winds and heavy rain). That’s what matters. Any fabric is good enough when new whereas the key thing is how long a fabric can maintain ratings comfortably above 600mm. Here we see the X-Mid fabric on track to do that for longer than any of these competitors.
In more detail, the blue fabric is from a competitor who claims it at 5,000mm and writes that it is “highly waterproof” and “will not degrade in it’s first year” but it actually starts out about 1,200mm and begins to decline right away so it reaches 720mm by the end, which is barely sufficient. The yellow and orange fabrics are from the same company and spec’d at 2000mm and 4000mm respectively. Those ratings are fair since they do start off quite high, and yet both drop rapidly after a certain point which shows you how useless these new fabric specs can be. Likely the coatings are thin or not that well impregnated, so once the coating starts to wear through the rating rapidly drops. The yellow one is questionable by the end while the orange one is still waterproof but on a worrisomely steep decline.
The grey fabric is the main fabric of a large competitor who uses it throughout their line and it shows good performance with the second highest end result and a moderately steep decline indicating it’ll still be waterproof for a while. Of all these fabrics though, the X-Mid fabric shows the most gentle decline because the coatings are so heavily impregnated. At 1,600 mm after 16,200 cycles, it is on track to remain waterproof for a much longer time and could likely repeat the entire test again while staying above 600mm. We rate this fabric at 2,000mm as a conservative number that reflects the post-wear results moreso than the new fabric, but note that it is actually more waterproof in the long run than these competing fabrics rated at up to 5,000mm. That’s really what you need to know if you’re concerned about reliable waterproofing.