Ultrasonic and induction welding can both be used to join self-reinforced polypropylene components.

In ultrasonic welding, a horn, vibrating at ultrasonic frequency, presses one substrate into the other causing frictional heating and local melting. Induction welding involves heating a conductive insert positioned at the joint line by using a high frequency generator which melts and fuses the substrates together.

Both induction-welded and ultrasonic-welded joints have been made, the latter to the same specification as the BS5350 adhesive joint test.

Both sets of joints have shear strengths comparable to adhesive systems, although induction welding results in less surface marking than ultrasonic welding, making it more suitable for cosmetic parts.