Heat fusion is a process used to join thermoplastics such as PP-R together. Rather than using glue, solder, or a mechanical connection and gasket, heat fusion physically turns the two pieces of plastic into one piece. The process is similar to welding, but doesn't require a filler material and, in the case of Aquatherm's specially formulated Fusiolen PP-R, heat fusion does not weaken the material at the point of connection. Aquatherm's heat fusion connections use a large joining area, making the connection at least as strong as the pipe itself, and often stronger.
Heat fusion works by returning the connection point to a melted state, the way it was during production. This allows the polypropylene chains to join together as the connection cools for a permanent bond, as if they were manufactured as one piece. This prevents any sort of chemical or physical weakness at the point of connection and results in a much lower instance of leaks or failures.