determining fabric type

Yes, there is such a thing as polyester ripstop fabric…but if your fabric is soft and silky, it's probably nylon (which was originally developed as a substitute for silk – think women's stockings!).

Often, what's written on the cardboard core in fabric stores is not accurate.

Valarie,
Thanks for the info. Too bad you can't trust what on the cardboard. I'll try to post some pics of it once I can get back to the store to buy a couple of yards.

After I ask for a price check on it, both of the older ladies at the cutting table where asking each other what on earth you would use a fabric like that for. Had to hold back on my geeky plans.

it could be polyester.

Plenty of polyester clothing out there. E.g. microfibre windshells, lightweight linings. ..

Some tent flys use polyester – it is much more UV stable than nylon

if it's the right weight and character, use it?

"if it's the right weight and character, use it?"

You bring up a good point. If polyester is more UV stable than nylon is, why is nylon so popular? is it because there is no such thing as a sil-polyester? I can't imagine that someone couldn't make such a fabric. most large commercial tent makers is a polyester that has at least a silicone coating on the outside.

Am I correct in thinking that polyester has less stretch than nylon does?

I guess I'm hijacking my own thread here, but now I'm curious why are cuben fibers and nylons the only fabrics that UL backpackers use? Why are polyesters generally shunned?

Nylon is typically more abrasion resistant and generally stronger than polyester of the same weight and construction.

is available
e.g.
http://www.extremtextil.de/catalog/Ripstop-Polyester-silicone-coated-40den-60g-sqm-2nd-choice::2188.html

more on that site…

Paramo favour Polyester over nylon for their clothing (inc mountaineering outerwear).

Seems to last well enough

One commonly-used method for identifying fabric type is to simply set light to a small piece, and carefully smell the fumes, and examine the residue.

Google for 'fabric burn identify' gives this amongst the hits:

http://house-of-jo.blogspot.com/2013/10/identifying-fabric-burn-test.html

If you stretch the fabric over a frame and leave it outside for a bit, the nylon will wrinkle as the temp and humidity change, a polyester good for MYOG won't. I use inexpensive plastic embroidery loops from sewing shops to do this.

Most of my experience with testing polyesters was with Epic Malibu, the ripstop material that Black Diamond first used on its single wall small dome tents. It has considerable stretch on the bias, but less than nylon on the warp and weft (in the directions the threads run).

There are some very light polyesters used for sail cloth, kites and paragliders, but they tend to be very stiff and noisy, and are not very well waterproofed. A good example is "Icarex," which may be still available from a UK company, "The Highwaymen." The Gossamer Gear One was made of a better waterproofed and stronger sail cloth light polyester, I think.

The greater strength of nylon, coupled with its greater elasticity, makes it more resistant to tearing, but the downside is the sagging, especially when the nylon absorbs moisture, as it will the more the coating allows moisture to penetrate. The polyester is not as strong, so is heavier for the same strength, and can be found on the cheapest tents often used for car camping. Snow Peak did come out with a winter tent called the "Lago," last year that has a very light PU coated Polyester fly. This is one of the few times I've seen light polyester used for a backpacking tent intended for severe conditions.