OK so I noticed I was late for work, clocked in with two seconds to spare.

Anyway I would choose polyester(AKA Dacron) coated on one side for waterproofness(resistance) because it is very strong, very UV resistant without any treatment, very chemical resistant, it doesn't really stretch much, it is slightly stiffer than nylon, almost as abrasion resistant as nylon, and most of all I have a set of medium sized panniers made of polyester that were bought over 15 years ago and, though slightly faded, they remain full strength.

Nylon is more abrasion resistant(esp. Cordura and other air textured nylons), stronger when subject to shock loads (like a mountain climber falling) because it stretches(think bungee), more limp for a given fiber size, and more common than polyester in outdoor fabrics. However nylon does tare very easely after a fair amount of use in the sun.

Tin cloth, wax/oil finished cotton or hemp canvas or twill is quite strong, very stiff, very waterproof, fairly low cost, easy to seam seal (just rub on some waxoil stuff), doesent unravel or catch on pointy things (smooth[ish] sealed surface), looks good without dye, undyed it won't fade, UV proof, and easy to clean (just wipe off with a wet rag). It is a fair bit heavier for equal strength, however most luggage fabric is more than strong enough, so it may be about equal weight when aiming for the same stiffness, you must test this 'cause I dunno. It may be tougher than most home sewing machines.(depending on the exact weight of the fabric and of course the individual machine.)

Spectra (AkA ultra high molecular weight polyethelene) is very strong and low stretch but not at all resistant to UV.
Kevlar is quite expencive, hard to cut, and if I recall has only moderate UV resistance otherwise great stuff.
Carbon fiber is just so stiff it would be ridiculus to try to sew.(not the fiber reinforced plastic, the actual fabric that reinforces the plastic. Same for glass fiber fabric. Neither would be fun if some frayed bits got into your cloths.

Weave choice is about a few factors: surface feel, a stable structure to work with(so it's not parallelagraming and so on), drape-ability or the ability to take compound curves, stiffness, to some degree strength, and the look. Generally a more stable weave is stiffer and less able to take compound curves.
Plain 1*1 is the most stable and least able to take compound curves, and it has corse feel; 2*2, 1*2, 2*3, 1*3 or 3*3 plain weaves are called basket or oxford weaves they are almost as stable as 1*1 but feel smoother and can take slightly more compound curving than a 1*1, they also tend to be stronger because the strands aren't being bent up and down as much or as tightly, the 1*2 and other unequal types have a slight ribbed feel. Ballistic nylon weave is a 2*2, I think, but woven much closer in both directions.
Twill and satin weaves are a bit more complex. Twill results in a fairly stable fabric that can take a decent compound curve, twill has the diagonal lines, denim is a type of medium weight twill. Satin is very shapable, but hard to work with because it's not very stable, satin is very smooth and strong as strands don't weave up and down much.


Weight or denier of the fabric depends on what you want, of course, heavy or high denier is not only stronger(how strong do you really need) but stiffer, and more abrasion, tare and cut resistant. Light weight fabric is of course light, but also less expensive, limper, and more prone to puncures, tares and cuts. I wouldn't go below 400denier polyester or nylon, or below 8oz waxed canvas(before waxing, 8.5-9oz after). 600 denier or 12.5oz(after wax, 11oz before) would be my choice I think.

Of course if you want fully rubberized/plasicized fabric like Ortleib uses, most of this is N/A.

Silboat sails are generally made of Dacron polyester and seems to be fairly stiff in the heavier weight sails, try hiting up a local sailmaker for some scraps.

Dumpster diving rocks(not in places that have rotten stuff like food markets and resturants)