HVAC tape it’s an aluminum foil tape. It’s very tacky and ridged.Never saw what the tape was he was using. Don't think it was duct tape maybe ?
Interesting video, Jim. When I was building model cars as a kid I would make my own filler using liquid model glue. Dissolve tree pieces in it until the desired consistency is reached. I bet the acetone is a lot cheaper---LOL! The styrofoam is a new one on me.I’ve used the acetone and small pieces of styrene to make plastic for model train repairs. The melted styrofoam was interesting.