Inversion hazards:

Underwater:

If there is more air in the drysuit than is needed to counteract “squeeze” on the undersuit, that excess air creates a "bubble" which moves to the highest point of the suit, which in an upright wearer is the shoulders.

Drysuit wearers wearing loose baggy suits need to keep their legs at level or below their waist. When inverted, with the legs above the waist, the bubble quickly moves top the highest point, the legs.

If the suit is being used correctly, the bubble is small and its movement is not important. The bubble may be large if a diver has ascended without venting the suit or the diver is over-weighted and extra air has been put in the suit to make the diver neutrally buoyant. The movement of a large bubble can be a problem; it balloons the legs and it may inflate the thin rubber booties causing the fins to pop off, losing them in the water. Also, as the drysuit vents are most often situated at the top half of the diver, it is impossible to vent the suit while inverted. If the diver is positively buoyant, there is an increased risk of a fast ascent to the surface.

The size of the bubble can be minimised by being correctly weighted and venting the suit on ascent. Some divers ensure that the bubble remains at the top of their body by using the buoyancy compensator to counteract any excess weighting and keeping the minimum air, to avoid squeeze, in the suit.

For an inexperienced diver, ballooning of the legs can cause a loss of control that may to lead to panic and an inability to flip upright again. The recommended solution is for the wearer to bend at the knees, reach up and grab the legs, do a somersault to flip upright again and vent the suit if needed by opening the neck seal.

Surface:

Surface drysuit users can face a similar inversion problem. The problem is more acute when not wearing a personal flotation device (life vest) over the drysuit. For surface drysuit users, the inversion situation can be much more critical if no one is nearby to assist, since the wearer may be held upside down and unable to breathe, and may also have water run down into their nose while inverted.

It is not a problem for close-fitting neoprene suits, or hybrid suits with neoprene bottoms, which prevent air from easily moving into the legs of the suit. Wearers of baggy surface drysuits can mitigate the problem by venting out as much excess air as possible before entering the water. This is typically done by crouching down and leaning forward, wrapping the arms around the knees, and then having an assistant zip the suit shut while it is stretched out tightly. Excess air can also be "burped" out of the neck seal. Some baggy suits have elastic "gaiters" that can be pulled snug around the legs to help prevent this inversion event from happening.