The highest percentage of the time the cause of leaks in the HD vacuum press is a dirty membrane. Due to the unique design of the HD vacuum former the membrane itself creates the seal. Any debris accumulation on the HD membrane may cause the press to slowly lose vacuum. The debris comes from a dirty work area, dust floating in the air, and/or small bits of the thermoform-able material you are vacuum forming. This debris and dust adheres to the membrane due to static build up on its surface caused by air rushing across the surface every time vacuum is applied.