Abstract: A heat exchanger (10) comprising a plurality of plastic tubes (12) arranged in a series of mutually parallel rows and a pair of plastic collector plates (14) bonded to the respective ends of the said tubes (12). Each collector plate (14) is formed by a plurality of plastic terminal elements (22), each of which has at least one set of semicircular seats (24 and 26) suitable for receiving the ends of a row of tubes (12). The said semicircular seats (24 and 26) of each terminal element (22) are separated from each other by bonding portions (28 and 30) suitable for welding to the corresponding bonding portions of a complementary terminal element along a welding plane (34).