Most reliable and affordable--Salk Sani-Pants.  These are listed as being made of nylon--they once were, but I'm pretty sure they're now made of polyester.   If Betty Mills has really old stock you might get nylon--?   They used to be made in USA--not sure they still are--online catalog descriptions rarely get updated.  They should be hand-washed alone, as they will be covered with hard-to-remove pills it they are washed or dried with cottons.  Hand-washing is easy and they'll last much longer if not machine washed or dried.  Because they have no absorbent lining they air-dry very quickly.  If not washed immediately after use the leg binding might hold odor.  The leg and waist bindings are covered, making them comfortable and both easy and painless to put on and remove--anyone who buys briefs with bare elastic waist and legs will be sorry.  I don't recommend the snap-side version--being located at the sides they are likely to be uncomfortable and possibly leak, but if changing without undressing is important they might be okay.  The size runs a bit large, so if you have a 30-32 inch waist the size small should work--the leg on size medium will fit too loose for leg circumference less than 18 inches.  They are roomy enough to fit over thick diapers or pad/liners.   They are more substantial and durable than most light-weight plasticized fabric or vinyl briefs.  Because they do not "breathe" (like PUL does) they hold perspiration and heat, but generally this does not become an issue if they are going to be changed soon enough anyway.