From the Super Mario Wiki
The Sweatmore Superhotpants are an upgraded version of the Sweatmore Hotpants found in Wario: Master of Disguise. They are located inside a purple treasure chest in Sweatmore Peak. In Episode 7, the chest is in the bottom-left corner of the volcano. In Special Episode Part 4, it is submerged in the magma in the first room. The Sweatmore Superhotpants allow Wario to travel through all of the magma in Sweatmore Peak without taking damage, including the more intense magma in the lower levels of the volcano that the basic Hotpants don't protect against.
Wario can lose the Sweatmore Superhotpants if he is attacked by a Snackeral, though if he has both kinds of Hotpants, the Snackeral will steal the basic Hotpants rather the Superhotpants. If Wario loses the Superhotpants, he must go back to where they were originally found to obtain a replacement for them.