Spearfishing Wetsuit Guide for Australia

Ask ten spearos what thickness spearfishing wetsuit you need and you'll get ten answers, and the annoying part is that most of them are right. One bloke dives a 3mm through a Victorian winter. Another wears a 5mm in Sydney and still gets cold.

That's not people being difficult. It's a sign that the thickness chart you're seeing is missing about half the variables that actually decide whether you're warm.

So we start with the stuff those charts leave out, then get to the numbers.

Why The Thickness Charts Let You Down

Water pulls heat out of you far faster than air at the same temperature. Water has much higher thermal conductivity and heat capacity than air, so immersion strips heat many times quicker than standing around in the same air temperature. That's why 20 degree water feels nothing like a 20 degree morning.

What the charts skip is that the rate you lose that heat depends heavily on you. Body composition and subcutaneous fat meaningfully change how fast you cool in cold water, and body size matters on top of that.

You see it plainly whenever divers compare notes. One diver reports being comfortable in a 3mm two piece in water around 8 degrees, and mentions being a big unit as the reason. Another says they max out at 5mm in Southern California and still wish they had a 7mm some weeks. Someone diving the western Mediterranean runs a 7mm at 17 degrees and calls themselves spoiled, while divers in Scotland and New Zealand are in 5mm at half that temperature.

Nobody there is wrong. They just have different bodies and different definitions of cold.

Acclimatisation is real too. Repeated cold water immersion produces genuine habituation, blunting your shivering and cold shock responses over time. Dive the same water every weekend through autumn and you'll handle it noticeably better by July than someone who has just flown down from Cairns.

Open Cell Or Closed Cell

What Open Cell Actually Is

A closed cell suit has a fabric lining on the inside. It slides on reasonably easily, it's tough, and it lets a thin layer of water sit between you and the neoprene.

An open cell suit has no lining on the inside. The raw neoprene sits directly against your skin and effectively suctions onto it, so almost no water moves through. Less water movement means less heat carried away, which is why an unlined suit runs warmer than a lined one of the same thickness.

The trade off is that you cannot pull it on dry. You need soapy water, dedicated suit lube or hair conditioner to get into it, and you need to be gentle doing it.

The Rough Conversion

Here's the practical bit divers actually use. An open cell suit is meaningfully warmer than a closed cell suit of the same thickness, but not warm enough to skip a whole size.

As one diver put it, a 3mm open cell is warmer than a 3mm closed cell, but it's not quite a 5mm. Another reckoned a 3mm open cell matches a 5mm semi dry. Treat open cell as buying you roughly half a step to a full step of warmth, and size from there.

What It Costs You

Open cell is more fragile. The exposed inner surface tears if you drag it on, fingernails go straight through it, and a rushed job getting changed at the car park is how most suits die.

If you're new, a closed cell suit is a perfectly sensible first suit and you'll be less precious about it. Most divers who move to open cell don't go back, but there's no rush.

What Thickness For Australian Water

With all those caveats stated, you still want a starting point. This is what works for most divers around the Australian coast, assuming open cell neoprene and a couple of hours in the water.

Treat those temperature bands as ballpark rather than gospel. They shift year to year and current, and the honest move before you spend real money is to check current sea temperatures for the spots you actually dive rather than trusting a national average.

If you're only buying one suit and you dive the southern half of the country, a 5mm is the honest all rounder. One diver who spears the Victorian south coast runs a 5mm from April through to November and swaps to a 3mm over summer, and says the thing that kills him in a 5mm in January isn't the water, it's the walk down the beach.

That's worth taking seriously. Overheating on the surface and on the walk in is a genuine cost of going too thick, not just a minor annoyance.

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The Stuff That Matters More Than Millimetres

Your Hands, Feet And Head

This comes up constantly and it is the single most useful thing here. Divers who've tried both routinely say gloves and boots do more for their comfort than adding thickness to the suit.

One diver in Monterey said he stays toasty in a 5mm where most people insist on a 7mm, and put it down to gloves and boots mattering more. Another described being fine overall but having to pull his gloves off once the water crept up. Your extremities are where you notice cold first and where the cheapest fix lives.

A hood is the other one. Get a suit with an attached hood if you dive anywhere south of about Sydney, because an unhooded 5mm is not the same suit as a hooded 5mm.

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How Long You're Actually In For

Every thickness chart quietly assumes a dive length and never tells you what it is. A suit that's fine for 45 minutes can be miserable at hour three.

As one diver put it, a 5mm will keep you warm for hours where a 3mm won't, even in warmer water. If you're the sort who gets out when the tide turns, size for the shorter session. If you're doing long drifts or working a reef all morning, go up.

Depth Steals Your Warmth

Neoprene is foam, and foam is mostly gas bubbles. Take it down and pressure squeezes those bubbles smaller, so the suit gets thinner and insulates less exactly when you're deepest. Testing under hydrostatic pressure confirms it, with measurable thickness loss and falling thermal resistance by five metres and considerably more by twenty.

Add a thermocline on top of that and the difference is stark. One diver described being comfortable at the surface and hitting what felt like a brick wall at twenty metres, with everything becoming harder including his breathing.

If you spend most of your bottom time deep, factor that in rather than sizing off the surface temperature.

Layer Up Instead Of Buying Thicker

Before you spend on a 7mm you'll wear six weekends a year, look at layering. It's more flexible and usually cheaper.

• Long john plus jacket. A 5mm long john under a 5mm jacket gives you roughly 10mm over your core where it counts, while your arms and legs stay mobile.
  

• A thermal vest or core warmer under your existing suit. Small, cheap, and it targets the area that actually drives how cold you feel.
  

• A hooded vest under a two piece if your suit doesn't have a hood.
  

• Thicker gloves and boots before anything else, for the reasons above.
  

Layering also means one suit stretches across more of the year, which beats owning two suits you half like.

Fit Is Where Suits Live Or Die

A cheap suit that fits beats an expensive suit that doesn't, every time. Gaps at the neck, wrists, ankles and lower back let water flush through, swapping the water you've warmed for cold water from outside, and that flushing is what makes you cold.

What you're after is snug everywhere without anything pulling. If it restricts your chest or shoulders it'll cut into your breath hold and wear you out, and if it's loose anywhere it'll flush.

Check the size guide properly rather than guessing from your shirt size, and if you're between sizes on a two piece, remember you can mix. Plenty of divers need a different size top to bottom, and pretending otherwise is how people end up cold.

Smaller and younger divers tend to feel the cold sooner than big adults, and a kid in a baggy hand me down will be cold no matter how thick it is. Suits actually built for them are in the kids range.

One Piece Or Two

Two piece suits, usually a long john or high waisted pant with a hooded jacket, dominate spearfishing for good reasons. You get double thickness over the core, an attached hood, and the ability to strip to just the pants when it's warm.

One piece suits are quicker to get into and have fewer seams to leak, but they're less adaptable and rarely come hooded.

For most Australian spearos, a two piece is the better buy.

Your Weight Belt Changes With Your Suit

This one is a safety point, not a comfort one. Neoprene floats, so a thicker suit needs more lead to get you down. Divers switching between a 3mm and a 5mm notice it immediately.

The trap is that the same compression that costs you warmth also costs you buoyancy. The suit that floated you at the surface floats you far less at twenty metres, which is the wrong direction for a breath hold diver.

That's why freediving guidance is to stay positively buoyant at the surface and only reach neutral somewhere around ten metres. If you black out, you want the water pushing you up rather than down. Never weight yourself heavy enough that you sink when you stop kicking, and recheck it any time you change suits, change thickness or add a vest.

You'll also hear experienced freedivers say flatly not to freedive in a drysuit. Take that seriously. It's a scuba tool, and managing a variable air volume on a breath hold is a problem you don't need.

Camo And Colour

Camo isn't just marketing, though how much it matters depends on how you hunt. If you're ambushing fish on a reef and holding still, blending into the background genuinely helps. If you're drifting bluewater, it matters less.

The counterintuitive part is which colours disappear. Water absorbs red wavelengths first, so red goes dark and neutral at depth rather than standing out, which is exactly what you want on a suit. We've written about why we use red camo if you want the longer version.

Match the pattern to where you dive. Weed and reef patterns for temperate kelp and rock, blue and lighter patterns for clear tropical water.

Making It Last

• Rinse it in fresh water every single time. Salt crystals work away at neoprene as it dries.
  

• Use lube going on and coming off. Most open cell tears happen during a rushed change.
  

• Dry it inside out and out of direct sun. Sun is harder on neoprene than salt water is.
  

• Hang it on a wide hanger or fold it loosely. A wire coat hanger will crease and eventually crack the shoulders.
  

• Glue small tears straight away with neoprene cement before they run.
  

Do those five things and a good suit lasts years rather than seasons. If something does go wrong with the neoprene or the stitching, our 12 months warranty on wetsuits covers where you stand.

What The Evidence Backs Up

• Water strips heat far faster than air, through much higher thermal conductivity and heat capacity.
  

• Your body composition genuinely changes the answer, so two divers in the same water need different suits.
  

• Cold habituation is real, which is why regulars handle winter better than visitors.
  

• Neoprene measurably compresses under pressure, losing thickness and thermal resistance by five metres and more by twenty.
  

• Thicker suits need more lead, and suits lose buoyancy as you descend.
  

• Positive buoyancy at the surface is standard freediving safety practice, not a preference.
  

• Red is absorbed first underwater, so red camo reads dark at depth.
  

• Flushing through a loose fit is what makes you cold, which is why fit beats price.
  

• One thing to check yourself. We could not tie the regional water temperatures beyond Sydney to a single authoritative source, so treat that table as a starting point and check your local readings.
  

What To Do Next

If you're buying one suit for the southern half of Australia, start at 5mm open cell, two piece, hooded, and add a vest for the worst of winter. If you're up north, a 2mm or a lycra suit will cover most of your year.

Have a look through the wetsuit range once you've settled on a thickness, and read our guide to picking a suit for any water temperature if you want a second opinion on the numbers.

For warm water and stinger season up north, the stinger lycra suit does a job neoprene can't, giving you cover without cooking you. If you want to understand what makes a suit warm beyond raw thickness, our piece on titanium lining is worth a read.

And don't forget the cheap wins. Gloves and boots live in accessories, and dive shirts for layering are in apparel.

The Short Version

• Thickness charts ignore your body, your dive length and what you're used to, which is most of the answer.
  

• Open cell is warmer than closed cell at the same thickness, worth roughly half a step to a step.
  

• 5mm is the honest all rounder for the southern half of Australia, 3mm for summer, 2mm or lycra up north.
  

• Gloves, boots and a hood do more for your comfort than adding millimetres to the suit.
  

• Neoprene compresses at depth, so you're least insulated when you're deepest.
  

• Layering beats buying a thicker suit you'll wear six times a year.
  

• Fit matters more than price, and a flushing suit is a cold suit.
  

• Thicker suit means more lead, and stay positively buoyant at the surface.
  

• Rinse it, lube it, keep it out of the sun, and it'll last years.
  

Get the fit and the extremities right and the millimetres mostly sort themselves out.