... 4.Inner wall is smooth,quick flow Composite pipe PPR-Steel pipe Size(mm): 20,25 32,40,50, ... heat conductivity, heat preservation, energy conservation, easy installation, dependable hot melted connection and recyclable materials.2. Unlike copper-plastic composite pipe, PP-R pipe ... system and air-compression pipeline4. Exclusive use in solar energy pipeline Comparision of various piping material with PP ...