I would say 0.5 mm is a pinhole...how the heck did you measure this?---
anyhow, if you follow the instructions in the kit, you will make a mess. What I did was buy some wood glue, and glue the fabric to the inside of the bellows. BTW I painted the fabric black. (Why in the heck they send white fabric I have no idea!. Anyhow once the fabric was fastend and dried I put the rubber compound on the outside until it was all black. It brushes on gray, but will blacken when it dries. BTW let the bellows stand open for at least a week, if you close it sooner the rubber will stick to the walls and come off.