Don’t let cold water dampen your snorkeling or diving experience. Don a wetsuit to keep yourself warm. It will also ward off sun, scrapes and stings, and make you more buoyant.

Dive shops rent wetsuits, and tour operators often provide them for guests. Buy your own to get a better fit and to reduce the ick of wearing a used garment.

Before you take the plunge, consider:

* Action: Wetsuits come in a variety of styles and thicknesses. Some are better for one sport or another. Thicker suits are warmer but more restrictive. That’s okay for divers, whose underwater movements are slow and calculated. Surfers need to stay agile. Snorkelers don’t need the same thermal protection as divers because they hang out near the warmer surface.

* Style: Wetsuits are made from neoprene, a synthetic rubber shot full of tiny air bubbles. Full-length suits extend to wrists and ankles, while “shorties” have short sleeves and knee-length pants. Farmer Johns (or Janes) are similar to overalls—wear them alone for paddling and wading, or with a jacket for diving. A rash guard is a lightweight polyester shirt worn alone for sun protection or layered under a wetsuit to add warmth.

Other features to look for: Hoods, knee and seat pads, and ankle and wrist zippers. Many wetsuits zip up the back, which takes a little practice to manipulate. A few of the newer-fangled ones are even battery-heated.

* Thickness: Wetsuits are described by the thickness of the neoprene, usually in millimeters. A 6mm wetsuits, for example, is ¼-inch thick. Some wetsuits have two numbers, such as 5/4mm. The first number is the thickness of the torso, and the second number is the thickness of the limbs. The torso part will always be thicker because that’s where you need the most warmth. The thicker the suit, the more space it will consume in your suitcase.

You’ll find plenty of charts that specify certain thicknesses for certain water temperatures, but they can’t account for the wind conditions on any particular day or your personal tolerance for cold. If you’re diving in warm water, you might be cozy in a shortie, but your partner could shiver in less than a full-length 5mm. Caps, booties and other accessories provide extra warmth and protection.

I seem to always be cold, but for snorkeling (my favorite water activity) I’m comfortable in a shortie and a cap.

* Fit: Wetsuits work by trapping a thin layer of water between you and the suit. Your body naturally heats the water, which acts as insulation. Gently pull the wetsuit on over your swimwear like you would a pair of pantyhose. It should fit snugly with no bagging. If too much water gets inside, it won’t get warm.

* Cost: An inexpensive shortie starts around $60. Good quality full-length wetsuits run between $200 and $700, depending on features. Custom fits and alterations are extra.