Why so much polyester?

[I'll be brief]

Why are so many swim briefs made from polyester and/or lined with it? There are so many great looking suits made with polyester. I can not wear polyester, I break out in a rash if I do. Of all the places to break out in a rash the bathing suit region has to be one of the worst. I am receiving an unexpected monetary windfall and would like to splurge on new suits and a pass to the local pool. Does anyone have any ideas on were to find polyester free suits?
Thank you,
I'll be brief