Which wetsuit for which water temperature?

I always dive in at least a long 5 mm suit, even in the tropics at 30 °C. I have never found it too warm. Your body is around 37 °C and is therefore almost always warmer than the water around it. Because water conducts heat much better than air, you constantly lose heat underwater, and after several dives a day, your core body temperature drops even faster. You hardly break a sweat. Anyone diving in a 7 mm suit at 30 °C will not feel like they are wearing a down jacket in the height of summer for a long time.

That is not a hard and fast rule. As the table below shows, even the dive centers do not all see things the same way, and the best way to find out what thickness is right for you is to discover it yourself. However, it does happen again and again that a dive has to be cut short because of the cold. I have never heard of anyone having to cut one short because they were too warm. My principle is therefore better too warm than too cold.

If the water is colder than 25 °C, I additionally wear an ice vest with an attached hood over the suit, the Waterproof O1 with 5 mm on the vest and 7 mm on the hood. What else I wear is described in My Diving Equipment, Part by Part.

The dive centers at the destinations in the Atlas usually recommend thinner suits. At 27 to 30 °C, they recommend Lycra, a shorty, or 3 mm; at 22 to 25 °C, a long 5 mm suit; and below 18 °C, 7 mm, a semi-dry suit, or a dry suit. At depth, it is often colder than at the surface, after several dives a day you get cold more quickly, and everyone gets cold differently.

What the dive centers recommend for each water temperature

The table summarizes what the dive centers in the guides recommend for the water at their destinations. The temperature is the monthly average at the surface.

Water	What the dive centers recommend	Example
28 to 30 °C	Lycra, rash guard, shorty, or 3 mm	Koh Tao from April to October, Cozumel from June to September
26 to 28 °C	3 mm; 5 mm for those who get cold easily	Koh Tao in winter, Cozumel, Red Sea in summer
24 to 25 °C	long 5 mm suit	Cenotes, Red Sea in December
22 to 23 °C	5 mm; some 5 to 7 mm with a hood	Red Sea in February and March, Malta in October
20 to 22 °C	5 to 7 mm	Lanzarote in June and November, Malta in June
18 to 20 °C	7 mm, usually with a hood	Lanzarote from December to May
14 to 17 °C	7 mm, semi-dry suit, or dry suit	Malta from December to April

The dive centers do not always agree on this. In Lanzarote, Viva Blue recommends 5 mm in summer, while Daivoon recommends adding an ice vest to the 7 mm suit for everyone who gets cold. At the Red Sea, a 5 mm suit is sufficient for some even in winter, while others recommend 7 mm. Use the table as a starting point, and ask your dive center before your trip what they provide. In my experience, the recommendations tend to be on the conservative side. If in doubt, take the suit from the row below.

It is colder at depth

In summer, there is a thermocline under the warm water at many destinations. In Malta, the sea is 26 °C at the surface in August, but only 18 to 21 °C at 30 m. At Sail Rock off Koh Phangan, it gets 3 to 4 °C colder below 25 m. Off Nusa Penida, the water is around 18 to 21 °C at depth from July to October, with thermoclines down to 16 °C, although the table shows 28 °C for Bali. There you will need at least a long 5 mm suit, 7 mm, or a hood if you get cold easily.

If you are planning deep dives on wrecks or pinnacles, take the warmer suit. At Koh Tao, for example, 3 mm is sufficient for the dive centers all year round, but some take 5 mm for the deep pinnacles.

Multiple dives, wind, and breaks

Anyone who dives several times a day will continue to lose heat with each dive. In Sharm el-Sheikh, a long 5 mm suit is sufficient in winter, but those who get cold quickly or dive three times a day take 7 mm or a semi-dry suit. Breaks also count. On the boat, you get cold in a wet suit in the wind, which is why dive centers in Sharm el-Sheikh, Koh Tao, and Cozumel recommend a wind jacket, sweater, or warm towel for breaks on deck in winter.

Long or short, hood or vest

In addition to protecting against the cold, a long suit also protects against the sun and jellyfish. At Koh Tao, after the band, a tight suit made of Lycra or neoprene protects against jellyfish. You should only go to the bull sharks off Playa del Carmen in a long suit with dark booties or socks. You lose a lot of heat through your head, which is why a hood makes sense in cool water. Coraya in Marsa Alam recommends a hood or ice vest to everyone who gets cold easily.

Gloves are only allowed at the Red Sea for protection against the cold, and the dive center chamber recommends diving without them. In Cozumel National Park, they are prohibited. In Lanzarote, the Cabildo dive guide recommends them at the wrecks of Puerto del Carmen against cuts.

Your own suit or rent?

It is best to bring your own suit because it has to fit. Anyone who rents should state their size when booking. In Sharm el-Sheikh, a long rental suit costs €12 to €14 a day after the band, a shorty €7 to €9. In Bali, the dive centers before Nusa Penida rent 5 mm from July to October, and 3 mm at the Gili Islands.

How warm the water is in the month of your trip is shown in Where to dive in which month?. For each destination, the monthly water temperature and the suit recommended by the dive centers are listed in the Arrival guide and the Plan Your Diving Holiday guide, which you can find via the Atlas.