Direct Vent Pro pipe lengths for gas appliances make up the center of your chimney venting system. Direct Vent Pro pipe lengths is designed to integrate perfectly with all other Direct-Temp venting products. The inner pipe wall is made from stainless steel and the outer pipe walls are made out of galvanized steel. The crimped edges allow the pieces to slide together with ease. The free floating inner liner allows the pipe expand and contract with high temperatures avoiding stress or gaps.