I require absolute waterproofness, so 30d silnylon is out.

Now the choice comes down to either 70d silnylon or PU-coated taffeta? Which one?

"...absolute waterproofness..." as in the pressure of one knee on very soggy ground - ~25,000 mm H2O?

Something like that.

I used PU-coated nylon. It feels more robust than silnylon and a lot less slippery. Well worth the marginal extra weight IMHO.

if you want 70D use the sil, awesome stuff!

-Tim

Well, I settled on PU-coated taffeta.

Does anyone know good source for the fabric?

Michael-

I have PU 70d in coyote brown with .75 oz coat, which is about as light as I would go if
you want higher pressure waterproof. $4 a yard, 58" width to send it with the 'mid.

I have some heavier 1+ oz/ yard sq. coated 70d too. Not light.

Dave

Dave,

Would .75 coat be able to handle, for example, standing water?

As for the heavier coat, how not light is not light? What do you estimate a 8 x 6 tub (to be used in your tarp) would weigh?

Edited by herzzreh on 08/02/2011 17:29:30 MDT.

You can check my math.

For 70d with a .75 oz coating finished weight of aprox 2.75 oz per
yard squared. HH after wear tested of 3515 mm

Allowing for 5 " sidewalls and a hem.
8.5X6.5 equals 55.25 square feet or 6.1 square yards.
6.1 X 2.75 oz equals 16.8 ounces or roughly 1 lb.

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With a heavier coating, say 1.5 oz you would add
6.1 X .75 equals 4.6 ounces for a total with the thickest coating
of 21.4 ounces. Richard's HH after wear testing was also 3515

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If you used some 70d with a .5 oz silicone coating,
which has the HH after wear testing of 3445, the total weight
would run about 15.25 oz.