"Resistant to penetration with a thick layer of fire retardant material."
These boots are a part of the Hardplate series and they have the highest physical and overall defense of any boots in SAS 4, with protection that's superior to the Titan MEM Trooper pants. However, it sacrifices movement speed, being the only boots to have a movement penalty, though that can be removed with the heavy gear skill (for Heavy class) or using the Machine Assisted augment on it.
These special boots are somewhat unusual as they can aid in tanking, whereas many boots have negligible defense without Body Armor Expert. Unfortunately, these are quite heavy, and they will slow you down, although not by too much. Being boots, these can be augmented with Machine Assisted, which will help to counteract the movement penalty.