Taper a Length of PEX Onto Your Foam Gun to Reach the Deep Gaps

The Problem

A foam gun's rigid barrel reaches maybe a forearm into a cavity. The gaps that actually need foam — behind frames, down inside stud bays, at the back of a void — sit past that, so the foam gets sprayed at the opening instead of into the gap, curtains over the front, and reads as filled when the back is empty.

The Technique

1. Cut a short-to-long length of PEX — underfloor heating pipe, any offcut — to suit the reach you need.
2. Push it onto the gun's nozzle tip so it seats with a friction taper.
3. Feed the tube into the gap and foam from the far end back toward yourself.

The tube gives you effectively a four-foot foam gun: the bead starts where the cavity actually ends, fills forward, and the overspray mess around the opening mostly disappears.