VEVOR Hard Pistol Cases with Pre-cut Lining, Waterproof & Dustproof Hard Gun Case for 5 Pistol, 18.9×16.3×8.5 in Lockable Pistol Case, Black

It comes from an automatic air valve, which is usually used when the temperature is high, too hot or too cold.

The pre-cut liner is a custom-made XPE material and the pre-cut foam is a hand-torn sponge.