On KoLmafia version r14945:
In modifiers.txt the Slimesuit bonus is listed as:
Slimesuit Cold Resistance: +3, Hot Resistance: +3, Sleaze Resistance: +3, Spooky Resistance: +3, Stench Resistance: +3, Damage Reduction: 10, Muscle Percent: +20
This looks very similar to the hardened slime hat...