I really need some help, I recently debadge my front bumper and filled with Fusor 142 plastic adhesive and then went over with a layer of Evercoat metal glaze putty and sprayed some 2k acrylic primer and finally painted the entire bumper. Unfortunately as soon as I threw it out on the sun it started growing air bubbles under the repair area
After some research I found this thread from 2006 where someone had the same problem http://autobodystore.com/forum/showthre ... per-repair
It leads me to believe I cant use Fusor plastic adhesive to fill the hollow area where the badge was so my question is what other material can I use? I would really appreciate any help.

First mistake, throwing it out in the sun. I'm sure you had trapped solvent pockets between those very "different" materials. I mean, essentially a polyurethane filler with a polyester material over that. Direct sunlight can quickly jack a surface past 160 degrees which forces the solvents to come out fast all at once, hence the bubbles. A better way to handle different materials like this is to let each material fully cure before moving on to the next.

Let's address the best way to do these type of "fill ins." In my opinion if you want a "bulletproof" way of doing this it is always going to be best to go the pick and pull and get another Subaru bumper, try to match up your same style with that same emblem area, remove the emblem, then cut out the area beneath it so you have a perfect weld patch of new plastic. Plastic welders aren't that expensive and do a great job of bonding these "similar" materials with NO compatibility problems. If you don't want to do that then your best bet is to use something like USC's Body Icing or even their more flexible, Pro Flex for a fill in like this. Pro Flex used to be called Thin Ice. There are also many other alternatives. Do some reading in the How To section here.... http://www.urethanesupply.com

Stay with the fusor repair material. But use it till the shape is exactly how you want it. Then let cure for 24 then prime and paint. I've found with 3M or Lord fusor. Tou have to let each application dry 24 hrs to be able to sand to a feather edge.
I've built out 4-5 inch sections ending on a edge and neverhad a problem. Except when I tried to rush it and not wait. Have made several urethane lip kits. Fit cars their not designed for.