Hercules weighs 5,200 lbs. in air. So, it needs some help with floating, or buoyancy with all that weight. It has a yellow, thick layer of syntactic foam on top to assist with buoyancy. The foam is made of small, hollow glass balls and a resin of epoxy that can withstand the heavy pressures of up to 4, 000 meters of water pushing down on it. It is considered as a positively buoyant vehicle which means that if it gets separated from Argus (i.e. cable breaks), then it will float to the surface instead of sinking to the bottom.
Institute for Exploration / Ocean Exploration Trust