Often forced air is used to improve convection, sometimes focusing the heat on one component of the item.
Some are built into a production line or are integral with machinery that also applies the shrink film.
Roller conveyors can be used with polyolefin, PVC, and shrink polyethylene films.
The space in between the rollers is filled with hot air from the bottom of the tunnel to shrink the film layer around the object, creating a sealed package.
When used with polyolefin and PVC based films the rollers are called "live" or spinning.