Vacuum bagging is a process that requires unique materials and processes, but can be simple to operation in an ongoing basis.

There are many advantages to vacuum bag molding, a few of which include:

  • Improved resin/glass ratio
  • More consistency across the laminate and part -to -part as compared to open layup
  • Containment of air emissions from the resins

As compared to hand layup and chop layup, there are a few disadvantages, including

  • Higher consumable material cost
  • Higher capital equipment


  • Difficulty with superior surface finish

Some parts are more suitable for vacuum bag molding than others. It also depends upon which process it is being compared with.

Vacuum bag molding requires an extremely tight seal between the mold and the bag. Molds with multiple pieces or holes for inserts can be difficult to complete a seal.

Parts that are overly large and complex can present challenges with placing resin and reinforcement before the cure cycle starts. The bag must be completely sealed and under full vacuum before the curing cycle of the resin begins.

The basic premise of vacuum bag molding is that the air is removed from the bag, allowing the atmosphere (air on the outside of the bag) to push the bag onto the part on the mold, compressing the layers of resin and reinforcement. Many misinterpret the process as “sucking the extra resin out.” We are merely allowing the laminate to be compressed by the weight of the air above us in the atmosphere to consolidate it before cure. The excess resin is usually absorbed by extra layers of sacrificial material inside the bag.