Why divers get cold
Water conducts heat away from your body many times faster than air at the same temperature. Even in tropical water around 28 °C, you lose heat on every dive, and over several dives a day that adds up. Being cold is not just uncomfortable: it raises gas consumption, makes fine motor tasks harder, and is considered a factor that can increase decompression stress.
Exposure protection slows that heat loss. Choosing the right suit is a balance between warmth, freedom of movement and how much weight you need to carry.
A practical guide by temperature
Everyone feels cold differently, so treat these ranges as a starting point rather than rules.
Above about 28 °C, many divers are comfortable in a rash guard or a 3 mm shorty, although a full 3 mm suit still protects against stings and scrapes.
Between about 24 and 28 °C, a full 3 mm wetsuit is the most common choice, with a 5 mm suit for people who feel the cold or do several dives a day.
Between about 18 and 24 °C, a 5 mm full suit is typical, often with a hood and boots.
Between about 14 and 18 °C, a 7 mm suit or a semi-dry suit, with hood and gloves, becomes the norm.
Below about 14 °C, many divers move to a drysuit, which keeps you dry and lets you add insulating layers underneath. A drysuit needs its own training.
Remember that temperature is often lower at depth than at the surface, especially below a thermocline, and that wind on the boat between dives can chill you as much as the water.
Small additions that make a big difference
A hood or hooded vest adds a lot of warmth for little bulk, because a large share of heat loss happens from the head and neck. Gloves and boots protect your extremities, which get cold first.
Fit matters as much as thickness. A suit that is too loose lets water flush through it, and you lose the thin layer your body has warmed. A suit that is too tight restricts breathing and circulation.
Between dives, take off a wet top layer, wear a windproof jacket and drink something warm. You will start the next dive warmer and use less gas.
Weighting changes with every suit
Neoprene is full of tiny gas bubbles, so a thicker suit floats more. Moving from a 3 mm to a 7 mm suit can mean several more kilograms of weight, and a drysuit with thick undergarments more again. Fresh water and an aluminum tank change the answer too.
Do a weight check whenever you change suit, tank or type of water. At the surface with an empty BCD, holding a normal breath, you should float at eye level, and sink slowly as you exhale.
Let your log guide you
The best guide to your own comfort is your history. When you record water temperature, the suit you wore, your weights and how you felt, you build a personal table: you will know that you were cold in a 5 mm suit at 20 °C, or that 4 kg was right with your 3 mm suit in salt water.
Frey Dive records water and air temperature, the gear you used and your weights with each dive, so the dives you made in similar water are easy to find. Before a trip, a quick look at similar dives tells you what to pack.