FOSTER FLEXTRA Sealant is a one component, butyl rubber based product used as a vapor barrier sealant in the joints of cellular glass, polyisocyanurate (PIR), urethane and phenolic foam board stock insulations. It remains soft and flexible, preventing damage to the insulation due to thermal cycling through a wide range of temperatures.

FLEXTRA Sealant is primarily used with low temperature insulation to prevent the migration of water and water vapor into the insulation system via butt joints.