Those guys are wearing Mustang suits. Those are basically thick flight suits sewn over a loosly fitting wet suit. They are used as anit-exposure suits. Here is what my regulations say about its wear:
AFI 11-2MH-53 Volume 3,
6.4.4. Personnel will wear anti-exposure suits on any preplanned over water flights which is beyond
autorotational distance from land and the water temperature is 50 degrees Fahrenheit or less. If water
temperature ranges between 51 and 60 degrees Fahrenheit, the unit/mission commander may waive or
extend the anti-exposure suit requirement after conducting a risk assessment considering the following
factors:
6.4.4.1. Climate zone and existing weather throughout range of flights.
6.4.4.2. Operational requirements.
6.4.4.3. Number and type of aircraft in formation.
6.4.4.4. Time of flight over water.
6.4.4.5. Risk, based on aircraft load and mission configuration.
6.4.4.6. Location, availability, and capability of search and rescue (SAR) forces, (consider anticipated
time in the water prior to pick-up).
6.4.4.7. Winds and wave height and their impact on SAR.
6.4.4.8. Altitude and distance from land.
6.4.4.9. Anti-exposure suits are not required when only the approach or departure is flown over
water.
These suits are okay if the air temperature is just right. If it is to warm, you burn up. Even when it is cold, you can start to sweat and they don't breath that good so you get cold anyway.