Mastic sealing tape provides an airtight seal between the vaccum bag and the mold. Tape may also be used to seal the point where the manifold enters the bag and to repair leaks in the bag or plumbing.

The better the airtight seal between the mold and bag material, the smaller the pump you’ll need. Poor seals, or material which allows air leaks, will require a larger capacity pump to maintain vacuum pressure.