Abstract: A foam duct is provided. Among other applications, it may be used in automotive HVAC systems. The method of making this duct reduces material waste and provides an unexpectedly reliable joint in a duct at a sharp or rounded corner. In place, the airflow further supports the joint. In the method, a first portion of a hollow pre-duct is joined with a second portion of a hollow pre-duct by bending the portions at a cut-out positioned between the portions. The bending is complete when the portions form a mechanical connection, which may be signaled by tactile or audible feedback.