Polyester/Lycra vs. Nylon/Lycra

[Torchwatch]

Is it the polyester fabric that causes the hives issue or the elastane in the Lycra (making it stretchy and skintight) that causes the issue?
Many tents and lightweight waterproofs are now made of polyester.
Aussibum were making some swim briefs in nylon, I bought some, it's kind of retro going back to pre Lycra days.
If you have an issue with elastic in waist bands and leg holes on both swim and underwear briefs consider wearing Japanese fundoshi designs. The Japanese used to swim in fundoshi until VJ day 80 years ago on Friday. Japanese swim teachers used to grab kids by the rear strap of their fundoshi should they start drowning.
The fundoshi is worn like a thong, the original B&W version of the 7 Samuri shows men in fundoshi.