you just have to read the label
I have GE Silicone II it is 100% silicone as per the label
however there are some GE SIlicone II with mildew stuff in it, you dont want that one
after steph noticed that GE II had mildew stuff in it, I checked next time I was at home depot...there are TWO types of ge silicone II doors and windows...you want the one that does NOT have anti-mildew stuff....make sure its 100% silicone and none of that acrylic business