Question: Can you tell me more about the expected durability of the fly fabric. I see you use a really light 20D Sil/pu coated polyester. How does it compare to 20D silnylon in terms of abrasion resistance, strength, and uv resistance?

Answer: Probably UV resistance is the best place to start: it's very good. Better than nylon by a long shot. In fact if you used both side by side for a couple of weeks the polyester would be significantly stronger than the nylon. Not that most people should care (at least not much). I'll explain:

The PU (polyurethane) on the underside of a sil/pu fabric makes the seams tapeable and that's the norm for US products. The tear strength is going to vary all over the map from source to source but the exact fabric I use in the MoonLights (20D 3xrip sil/pu, ) starts out about 15% lower strength than 20D ripstop sil/pu nylon from the same company (10% less in the warp direction, 20% less in the fill). But here's the thing: no one actually bases their tear strength requirements or even their desires on what’s NEEDED because no one knows what that too-low number is. So we've gotten into a sort of tear strength arms race even though it's obvious that it's the tensile strength that a tent primarily needs (and all fabrics available are WAY overkill on tensile strength).

So I've taken it upon myself to ask repair departments of my clients (and Kelty, of course, when I was there) what, if any repairs they saw that were caused by the tear strength being too low. Tents age, UV damages fabric, surely there should be some indication of a lower limit to tear strength in use. But the answer was always no. No repairs ever because tear strength was too low. Actually is was quite striking. There were even tents sent in for repair that you could literally push your finger through which weren't being sent back to be fixed because of that; the customer hadn't damaged it and it was sent back for something else entirely!

As to abrasion resistance or puncture resistance, ALL the lightweight fabrics we use are just terrible – it takes the barest swoosh against a sharp rock or a gnarled tree to put a bunch of holes or a tear into a rainfly. About the only thing one can say about higher tear strength is that there's the theoretical possibility (and hope) that a tear won't propagate as much in a higher tear strength fabric. But prevent a tear? No way. This is when having some of the truly excellent repair tapes available can really save the day. I love modern repair tapes.

Probably now would be a good time to also mention that the acceptability of any particular tear strength depends on the USER and their expectations — especially as regards the floor. Because the MoonLights are made to be genuine backpack tents, they use 30D floors which are far LESS prone to accumulating little rips than the 15D and 20D fabrics used in the lightest tents available. But the flip side is that our 30D floors, are also MORE prone to accumulating little rips and tears than heavier fabrics like 40D (and heavier). No news there. So the tent feature - being lightweight and compressible - is responsible for the user's need to use, and be comfortable with those fantastic repair tapes we keep mentioning. This is part and parcel of the current set of tradeoffs of the MoonLight tents.

That said, if I get feedback from MoonLight tent owners that I've misjudged their desires, then I'll change the floor fabrics. But there's no shortcutting this process that I can see. (By the way, in case anyone is worried, a floor repair with one of the tapes we mentioned is extremely waterproof.)

Here’s a link to McNett’s “Tenacious Tape” under their Gear Aid brand
Here’s a link to Kenyon’s “
But some swear that this is the best one of all: “
Tear-Aid Type A
Hot tip: buy clear or white so the color matches automatically.

Side note: reinforcing stress points is absolutely necessary regardless of a fabric's tear strength or it will get ripped in use. Everyone seems to do at least a fair job of this so it's not really a differentiating feature.

Side side note: The only polyester fabrics, other than our own, that you’re likely to find in tents on the market are 68D and 75D fabrics which are much heavier than the 20 denier fabrics in the MoonLights ('D' means denier which is a measure of the yarn weight). That's not so surprising because the 20D fabrics in the MoonLights are THE lightest polyester fabrics that can confidently be used in tents (at this time). You might think that the next thing I’m going to say is something bad about 68D & 75D fabrics, but actually, I think they're terrific. They weigh more, but they're really inexpensive and perform way above their price point. You’ll find these fabrics in virtually all major brands’ larger tents and in their value-priced backpacking tents (running around $200 give or take). Sadly, polyester is mostly just used in the rainflies, the body and floor are still usually nylon. It’s a pity because having the body and floor expand and contract is not good: sometimes the tent can be ridiculously tight setting up and it actually makes the square footage of the floor smaller – up to 7% smaller - than it’s specs say it is. The reason is that since all tents are made in China, you can safely assume that they were made in high humidity and are therefore bigger in all dimensions than when they dry out completely – like in the Rockies or the Sierra, or in the Southwestern US just about everywhere.

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