Did I state it was substancial ?, the fact remains due to laws of nature, if 3 cases and set ups were identical apart from 1 was plastic and 1 was steel and 1 was alu, the steel rig would be cooler than the plastic rig and the Alu rig would be cooler than both rigs.

Do you not seem to grasp the hot air inside case although sucked out by fans does actually sink into the cases inside surfaces.

In nearly every good site and threads here you will see peeps tell of slight gains in temps due to soundproofing material, and at the end of the day I DID state you need to compensate right at start or my post.