I followed up on the Birkenstock sandal you thought was vinyl. I can understand your confusion believing EVA or ethylene vinyl acetate is vinyl because it looks the same and has the word vinyl in it.
I am allergic to blended materials because an element from rubber, Mercaptobenzothiazole, MBT, which is used to accelorate the blending process. For example it is used in poly-cotton, elastics and such. I react to MBT. This element is never listed as the final material you contact. I can wear 100% cotton, 100% silk, 100%polyester, 100% vinyl for example because this element derived from rubber is not used making this material.
Still hopeful, in the past I have tried EVA footwear and sadly learned that by the end of the day my foot pad will begin to burn.