Nonyl phenol. I'm sure there are other things...but I can't find them right now. Generally I don't think it is a good idea to thin epoxy...even though it is thinned straight from various suppliers. The more thinning agent that is used the more the epoxy will shrink. There are other issues as well, but this is all open to discussion. The link below has a lot of information about epoxy. I have avoided using their epoxy...hoping someone else would try it and then post an evaluation. I guess I'm going to have to give it a try.