Western polyrub inflatable seal for isolator door is made from high strength FDA approved silicone rubber which inflate radially outward . Because the shell of the unit is fabricated due to less gape and not machined, the machined acrylic or steel door will be made to a much tighter tolerance than the frame. This means there will be a enough seal gap.western polyrub seal is made with 25 % to 50 % inflation which cover that gap with 2 kg pressure