A & A Manufacturing Co. Of New Berlin, Wisconsin developed a patented vulcanisation process called Vulca Seal, in which layers of elastomer-coated fabric are bonded together under heat and pressure at alternating inside and outside pleats to form accordion-like bellows. The seams are then sealed using large fixtures to apply the proper pressure and walk-in ovens to provide the necessary heat.

The base material for the bellows is generally 1 mm thick hypalon coated polyester, and the shape of the units is reinforced by an external aluminium binding which helps prevent distortion from automatic washers and damage from everyday operation. The corners and stress points of the bellows are reinforced with aluminium edging.

The fully vulcanised A+A Gortite folding Bellows (link below) do not leak at the top outside corners, the vulcanised design is more robust than stitched Bellows and additional ‘pockets’ are not necessary between the folds at the outside corners. The bellows are therefore easier to keep clean. The bellows do not need to be externally sealed at the top corners after installation and therefore do not discolour in these areas.