Do you need a wetsuit for open-water swimming?

Wetsuits divide open-water swimmers into two cheerful camps: the people who would not get in without one and the people who think neoprene ruins the point. Both are right, depending on the water.

What a wetsuit actually does

• Warmth. West Yorkshire Fire and Rescue's open-water advice puts it simply: a wetsuit helps you stay warm so you can stay in the water longer. You still feel the cold, just less of it.
• Floating. Most swimmers notice they sit higher in the water in a wetsuit, with legs and hips lifted, which makes front crawl feel easier and resting on your back simpler. Many nervous open-water swimmers find this the bigger benefit.
• A softer entry. The UK Met Office's guide to cold water shock explains that cold water shock is an involuntary reaction to sudden cold, that it can happen in water below 15°C, and that a wetsuit or drysuit can help insulate you and reduce the risk. It also stresses getting in slowly and giving yourself time to acclimatise, wetsuit or not.

What a wetsuit does not do is make cold water safe or turn you into a stronger swimmer than you are. Our piece on cold-water swimming safety covers that side properly.

Temperature: the main decision

Rough, personal rules of thumb rather than official ones:

• Warm summer sea or lake. Many people swim without a wetsuit and enjoy the freedom. Too warm and a wetsuit becomes uncomfortably hot.
• Mild water. A wetsuit makes a longer swim more comfortable, especially if you are still getting used to open water.
• Cold water. A wetsuit is the sensible default for most swimmers. Keep swims short even so, and follow the safety advice of the venue.

Everyone feels cold differently. A thermometer reading means less than how you feel after ten minutes, and how quickly you warm up afterwards.

Events that require one (or ban one)

Organised swims and triathlons often set wetsuit rules by water temperature. World Triathlon's FAQ, for example, says wetsuits are mandatory for age-group athletes at 15.9°C and below, and forbidden above a warmer threshold that depends on age and swim distance, with the official temperature announced before the start. Mass-participation swims and swimrun races have their own rules, so read the event guide well before race day.

Swimming wetsuit, not surf wetsuit

If you do get one, get a swimming wetsuit. Surf and diving suits are built differently and restrict your shoulders. Swim wetsuits are thinner on the arms and shoulders so you can reach forward freely.

Fit matters more than brand. It should feel snug everywhere when dry, with no pockets of air at the lower back, but you should still be able to lift your arms over your head and breathe deeply.

Rent before you buy

Many open-water venues, swim shops and triathlon shops rent wetsuits by the session or the season. Renting lets you find out whether you like swimming in one, which size suits you and how often you will really use it. It also means you will not have an expensive piece of neoprene staring at you from the cupboard in February.

A few tips for the first swims:

• Put it on slowly, pulling it up in small sections, and use the fleshy part of your fingers rather than your nails.
• Get in gradually and splash your face before you start swimming.
• Expect the neck to feel snug at first; a good fit should not choke you.
• Rinse it in fresh water afterwards and dry it out of direct sun.