My mold is pretty strong, but I think it could be better. I've feared coming out the next day to see a crack in it. It also depends on the vacuum applied. I generally use less than 10" for everything, including most of my molds. 5" or 6" is plenty (more than enough!) for white foam.

Leaks are a major problem as the edges of the mold seem to puncture the material very easily. My homemade vacuum system cycles whenever it senses a 2" drop in vacuum. This bag (brand new) is leaking and making the pump cycle every minute. This bothers me as it is bad for the pump to do so a lot and potentially shortens its lifetime. Generally, I can get 10 to 15 min cycles. I think there are some small leaks in my system, but the bag is the most noticeable.

Michael