How a Wetsuit Keeps Scuba Divers Warm Underwater

Scuba diver in wetsuit and full gear stepping into the water from a boat.


Let's face it. Squeezing yourself into a black rubber suit in the blistering tropical sun isn't anyone's idea of a good time. In the Caribbean, most first-time divers are hesitant to don a wetsuit. The water feels so warm that they cannot imagine becoming chilled during a dive. Yet, water conducts heat away from the body about twenty times faster than air. For example, 78 degrees F may seem balmy (or even hot), but 78 degrees F in water will eventually cool a diver who does not use a wetsuit. Any water cooler than body temperature has the potential to chill a diver and even induce hypothermia.

Wetsuits also provide a certain degree of protection for scuba divers from accidental coral scratches or contact with other aquatic life. Remember that while it provides protection, a wetsuit (or drysuit) does not give a diver free license to touch or brush against coral or other organisms. Divers can usually do more injury to aquatic life than aquatic life can inflict upon divers.

How Wetsuits Work Underwater

Wetsuits trap a thin layer of water against a diver's body. While the diver still gets wet, his body rapidly heats up the thin layer of water trapped against his body. The water inside the suit rises to nearly body temperature. If the suit fits properly, the warm layer of water does not circulate away from the diver's body.

So how does a wetsuit make it possible for a diver's body to heat up the water filling the suit? Wetsuits slow heat loss due to a thick layer of rubber (neoprene) filled with tiny air bubbles. The insulating properties of the rubber/bubble combination reduce heat loss from the water in the wetsuit and therefore the diver's body.

The thicker and more insulating the wetsuit, the less heat loss the diver will experience. The better the fit, the less water will circulate out and be replaced by cool water that will need to be reheated by the diver's body. Wetsuit fit and thickness work together to keep a diver warm under water.

Wetsuits are not perfect. The warm layer of water trapped against a diver's skin still conducts some heat away from the diver's body, and it loses some of its warmth through the neoprene wetsuit. Given enough time, a diver wearing a wetsuit may still become chilled, depending upon the type and characteristics of his wetsuit. In colder temperatures or on very long dives, a wetsuit may not be sufficient to keep a diver warm, and a drysuit may be a more appropriate choice.

The Tighter the Wetsuit, the Warmer You Will Be

A wetsuit keeps a diver warm by trapping water inside the suit. A snug suit will more effectively trap and hold water against a diver's skin than a loose suit. A wetsuit that does not fit snugly will allow cold water to circulate into the suit, which will cause the diver to become chilled more quickly. Tighter is better — up to a point. A suit that is too tight across the chest will restrict a diver's breathing, which can be uncomfortable and even dangerous. A suit that is too tight on the neck may restrict blood flow to a diver's head, which can be dangerous both underwater and on the surface. A suit that is so tight that the neoprene is stretched thin will not be effective.

The Thicker the Suit, the Warmer You Will Be

Underwater, heat is lost through the neoprene layer of a wetsuit. The thicker the wetsuit, the less heat will be lost and the warmer the diver will be. However, thicker wetsuits tend to restrict movement, so divers will be most comfortable choosing the thinnest suit that will keep them warm in the anticipated dive environment.

The Deeper You Dive, the Colder You Will Be

The neoprene rubber in wetsuits is lightweight and flexible because it is manufactured with millions of tiny air bubbles sealed inside the rubber material. Because these air bubbles are completely sealed, the air inside them will expand and compress according to Boyle's Law. The deeper a diver descends, the more the air bubbles compress and the thinner the wetsuit becomes. Because a thinner wetsuit is less insulating, the deeper a diver goes, the colder he can expect to be. Divers may want to choose thicker wetsuits for deeper dives.

The Longer the Dive, the Colder You Will Be

While wetsuits do help to slow heat loss underwater, a diver's body still gradually loses heat over long periods of time. After long dives, a diver may feel chilled from this slow heat loss. Select a thicker suit for longer dives. 

Natural Insulation

While a diver's “natural insulation” is not a characteristic of the wetsuit itself, a diver's body fat will affect how rapidly he chills underwater. Very fit divers with a low body fat percentage will cool more quickly than divers with a normal percentage of body fat. Divers who have very little body fat may want to consider choosing a thicker suit than average divers diving in a similar dive environment.

Short Suits vs Long Suits

Short wetsuits (or “shorties”) expose a diver's lower legs and arms to the water. Short wetsuits still help to keep a diver comfortable in warm water because they cover the diver's torso, which prevents a great deal of heat loss. They are not as effective as long suits because more of the diver's skin is exposed to the water, accelerating heat loss.

A good wetsuit slows heat loss underwater to the point that a diver remains comfortable throughout a dive. Consider characteristics such as wetsuit thickness and fit, as well as the length and depth of the dive, when selecting a wetsuit for a given dive environment.