How to choose a wetsuit comes down to three decisions in order: fit first, then thickness matched to water temperature, then style. A suit that fits badly in 7mm neoprene will keep you colder than a well fitted 5mm, because a wetsuit works by trapping a thin layer of water your body then warms.
How does a wetsuit actually keep you warm?
A wetsuit does not keep water out. It lets a thin film in, traps it against your skin, and your
body heats that film. The neoprene itself then insulates, because the gas bubbles inside it conduct
heat poorly. Once you understand that, most buying decisions answer themselves.
The consequence is that fit is the dominant variable. If the suit is loose anywhere, water flushes
through, taking the layer you just warmed with it and replacing it with cold water you now have to
warm again. That flushing is why a baggy thick suit performs worse than a snug thinner one. The usual
leak points are the neck, the wrists, the ankles and the small of the back.
It also explains why neoprene loses performance with depth. Pressure compresses the gas bubbles,
so a 7mm suit at one hundred feet is thinner and less insulating than the same suit at the surface. You
get colder deeper, partly because the water is colder and partly because your suit has shrunk.
How do I match wetsuit thickness to water temperature?
Thickness is quoted in millimeters, often as two numbers such as 5/3, meaning five millimeters
through the torso and three at the limbs where flexibility matters more than insulation.
Local conditions are cooler than most newcomers assume. Water off Long Island runs from the low
fifties Fahrenheit in spring to the low seventies at the end of summer, and below the thermocline it can be
sharply colder than the surface reading suggests. Divers here are commonly in 7mm with a hood through
most of the season, and in a drysuit outside it. Site by site detail is on our
Local Diving page.
Err thicker rather than thinner for diving. A snorkeller who gets cold gets out; a diver who gets
cold is on a decompression schedule and cannot simply leave. Cold also degrades judgment and manual
dexterity well before it becomes dangerous, which is a poor combination at depth.
How can I tell if a wetsuit fits?
Try it on dry, and expect a struggle. A correctly sized wetsuit is difficult to get into and
feels slightly restrictive standing up. In water it loosens noticeably, so a suit that feels
comfortable in the shop is almost certainly too big.
Check specific places rather than a general impression. There should be no loose pocket in the
small of the back, no gap at the neck you could slide a hand into, no bunching behind the knees, and
no folds at the ankles or wrists. Raise your arms above your head: the suit should follow without
pulling the seat of the suit down or restricting your shoulders so much that reaching your valve
becomes hard.
Women and men are built differently enough that suits cut for the other are a common source of
poor fit, particularly through the torso length. Manufacturers vary considerably in their sizing, so a
size that fits one brand tells you very little about another.
When a drysuit becomes the honest answer
At some point the sensible answer stops being a thicker wetsuit. If you are diving cold water
year round, doing long dives, or getting cold in 7mm and a hood, a drysuit is the real solution
rather than another millimeter of neoprene.
A drysuit keeps water out entirely and insulates with the undergarments you wear inside it, so
you regulate warmth by changing layers rather than buying a new suit. It also adds a buoyancy control
surface, which is exactly why it requires its own training. Drysuit diving is a separate skill with
its own failure modes, and it is not something to teach yourself on a dive holiday.
The cost gap is real and so is the durability gap. A drysuit is a larger outlay that lasts longer
and can be repaired, where a wetsuit is cheaper and eventually just gets replaced.
Making a suit last
Rinse in fresh water after every dive, inside and out, and dry it out of direct sunlight.
Ultraviolet light degrades neoprene faster than salt does. Hang it on a wide shouldered hanger rather
than a thin wire one, which cuts a permanent crease into the shoulders over a season.
Do not fold a suit for long term storage, and do not leave it in a hot car boot. Heat and sharp
creases are what kill neoprene early. Treated reasonably, a good suit lasts several seasons of regular
diving; treated badly, it can lose noticeable flexibility within one.
Key takeaways
- A wetsuit traps a thin layer of water and your body warms it, so fit matters more than thickness.
- A loose thick suit flushes continuously and will leave you colder than a snug thinner one.
- The usual leak points are the neck, wrists, ankles and the small of the back; check those specifically.
- Neoprene compresses at depth, so the same suit insulates less the deeper you go.
- Local water is cooler than newcomers expect; 7mm with a hood is common through much of the season.
- Err thicker for diving, because a cold diver cannot simply get out the way a cold snorkeller can.
- A correctly sized suit is a struggle to put on dry and loosens noticeably in the water.
- A hood is the cheapest meaningful warmth upgrade available, and often beats buying thicker neoprene.
- If you are cold in 7mm and a hood, the honest answer is a drysuit plus the training it requires.
- Rinse, dry in shade, hang on a wide hanger, and never store a suit folded or in a hot car.
Rough thickness guidance by water temperature
| Water temperature | Common choice | Notes |
|---|---|---|
| Above 79F | 3mm shorty or full 3mm | Warm water travel; comfort rather than survival |
| 70F to 79F | 3mm full suit | Late summer local diving for many people |
| 63F to 70F | 5mm full suit, hood optional | Typical Long Island summer conditions |
| 55F to 63F | 7mm with hood and gloves | Spring and autumn locally; most divers here own this |
| Below 55F | Drysuit with appropriate training | Neoprene stops being the sensible answer |
Want to book a class?
Call (516) 872-4571. We teach at 490 Sunrise Highway, Rockville Centre, NY 11570.
Frequently asked questions
Should I buy or rent a wetsuit?
Rent while you are deciding whether you will keep diving, then buy. Fit is the dominant factor in warmth and rental suits are sized to a crowd, so your own suit is usually a noticeable upgrade rather than a luxury.
Is a thicker suit always warmer?
No, and this is the central point of how to choose a wetsuit. A loose 7mm flushes cold water continuously and will leave you colder than a well fitted 5mm that holds its warmed layer in place.
Do I need a hood?
In local water, usually yes. A large share of heat loss goes through the head, and a hood is the cheapest meaningful upgrade in warmth available. Many divers add one long before they consider a thicker suit.
What about gloves?
Useful for warmth and for protection on wrecks and rocky entries. The tradeoff is dexterity, so practice using your kit with gloves on rather than discovering the difference during a real problem.
How do I know if a suit is too big?
Look for a loose pocket in the small of the back, a gap at the neck, or bunching behind the knees. A suit that is comfortable to put on dry is almost always too large once it is wet.
Why am I colder deeper even in the same suit?
Pressure compresses the gas bubbles in the neoprene, so the suit is physically thinner and less insulating at depth. The water is usually colder below the thermocline as well, and the two effects compound.
How long does a wetsuit last?
Several seasons with rinsing, shade drying and a wide hanger. Ultraviolet light, heat and sharp folds are what shorten that, and a suit stored badly can lose noticeable flexibility within a single year.
Can I use a surfing wetsuit for diving?
It will work in warm water but is not ideal. Surfing suits are cut for paddling flexibility and lack the reinforcement at knees and seat that kneeling on a boat deck and wearing a harness demand.
