Hi paulineh
As far as allergies are concerned it matters not a jot which you choose, - as silverlady says they are both estradiol - but the compound (estradiol) has been manufactured from its constituents in a lab/factory and will be absolutely pure, and bear no resemblance to the original. You would not get any sort of soy allergy from them!
The difference between the two is the way the estradiol is applied and released from the adhesive. Evorel are much larger patches, Estradot are tiny in comparison and specially designed to hold and release the same amount of estradiol as the equivalent Evorel.
I have (almost) only ever used Estradot and would go for these any time - so much easier to check if they are stuck and only cover a little place on your bottom!
Hurdity x