Supple pants with elastic wasitband?

I believe the REI Sahara pants have elestic, with a built in web belt to tighten them where you want- Is this what you mean?

Yeah, that is more like it. I have been trying some of the Patagonia ones but find they do not do that well because they are belt only and do not fit my odd shaped body so well.

The North Face has basically the same thing with elastic and a built-in webbing belt (Paramount Convertible Pants). I have a couple of pairs and really like them.

I can find nowhere where it says they are supplex.

Campmor's "Trekmor" convertible pants have an elastic back waist for both their men's and women's convertible pants. I have a pair (women's) and they are really comfortable. Much lower price than most, too!

Thank you but I don't think these are made out of supplex either.

Is there some reason you insist on Supplex (a specific brand by DuPont, so it should be capitalized)?

There are similar nylon fabrics out there that, IMHO, perform just as well. I can't tell any difference between a Supplex garment I have and my Campmor Trekmor pants. It's like GoreTex and its various clones–some insist on the original while others of us find the clones just as good and a lot less expensive.