I use a squeegee for glassing and have no foam problems. It's tough to analyze with so many variables, like brand of epoxy, viscosity and glass. Make sure you pre-heat your epoxy for glassing so the viscosity is thin. The squeegee is for spreading the epoxy in the beginning. You would normally not want to press hard. Once the epoxy starts to set up, you would press a bit more so you are pressing the glass down against the wood so it is not floating and taking off excess epoxy. Sometimes I get a tiny bit of foam and I even used that to wet areas that need a little more liquid. it seems to just go away with a few strokes of the squeegee. I also use a brush on small areas and if I get any air entrapment, I dab the area with the brush to open up the fabric to let air out. I'll bet your problem is the viscosity of the epoxy. Heat it a bit.