Why make tents out of sil nylon anyways?

I think that's well said from what little I know.

My best (don't quote me on this) understanding/recollection of 'denier' is that it is some kind of measure of the individual fiber diameter. So, in a general way, by itself, it can give a general sense of the weight of one fabric vs. another, but in actual practice you need to get the actual weight per square area of one fabric vs. another with different weaves from different mills, etc. Some weaves may be tight or loose, etc.

Denier is the weight in grams of 9,000m (yes nine kilometers) of that particular fiber (30D= 9000m of 30d nylon)
Linear not square.
Franco

There it is. So, it does essentially relate to diameter/size of the fiber.

"The ultimate tent material would be flexible polyester, and not sag"

Polyester is weaker than nylon by weight. The stretch of the nylon is a prime reason
it holds up to shock loads so much better than polyester. Cuben Fiber is polyester, but
has a Spectra scrim to impart strength.

"would be highly vapor permeable and therefore not need a liner or inner tent"

Inner tents add extra warmth & decrease condensation, some arctic tents are triple
walled.

"would have a super HH, at least 3000mm"

Not needed for many uses. Many older tents made of cotton or uncoated nylon, had HH of below 500, some well below. They were very breathable and if were light enough, would be a good modern choice for some climates. For example, I spent dry comfortable nights during snow and mixed rain in Teepee's made of two layers of uncoated 30d built from old parachutes by Airforce Survival School instructors. Also have used similar one layer shelters, but with a fire inside to drive out moisture.

Franco – thanks for the spec info on denier – will try to remember.
On second thought, that's hopeless. Will copy and past your post and file it in my highly organized filing system.

David,
When I'm camped in the open above timberline at 11-13K feet, the wind is howling, the rain seems to be blowing in every direction except vertical and is creating instant ponds with their own tidal waves, and the tent is single wall, then I want at least 3000mm HH. No fair asking why the h*** I would camp there in the first place anyways. Maybe I broke my leg.

People lately seem to make a big deal about HH.
In the old days, we were fine with treated cotton, silk and others that had very little HH.

We would get some dampness and water on our no-DWR sleeping bags, mopping the walls of our tent from time to time. It was no big deal and you slept OK.

So what's the big deal?

"David,
When I'm camped in the open above timberline at 11-13K feet, the wind is howling, the rain seems to be blowing in every direction except vertical and is creating instant ponds with their own tidal waves, and the tent is single wall, then I want at least 3000mm HH. No fair asking why the h*** I would camp there in the first place anyways. Maybe I broke my leg."

I am a belt and suspenders person and I understand. I even owned a Goretex Sleeping
bag once and used it with a tarp AND a bivysack when on long spring trips above treeline.

I also wore a rubber rain suit OVER a Goretex one for a winter trip on the coast of the
Olympics. 5 inches of rain an hour gives one a new outlook on HH.

Waterproof pads play an important role too when used with light duty ground sheets.

I like layers, can you tell?