Before you spearfish — this comes first
- Get proper instruction before you spearfish. A recognised freediving or spearfishing course teaches the things that actually kill people in this sport, and reading about them is not the same as being taught them.
- Dive with a buddy, and dive one up, one down — one diver in the water, one on the surface watching them, every dive. A breath-hold blackout is silent and gives no warning; a watching buddy is the difference between an incident and a fatality.
- Stay inside your own training and experience. Depth and breath-hold times are personal, they change day to day, and nobody else's numbers apply to you.
- Understand the conditions before you enter the water: visibility, current, swell, tide, boat traffic and your exit. Conditions decide whether a dive is reasonable far more often than skill does.
- Use equipment you have been shown how to use, check it before every session, and be visible — a marked float and line are how boat traffic knows you are there.
- Never extend a dive for a fish. No catch is worth pushing a breath-hold, and the urge to take one more second is exactly what a blackout feels like from the inside — which is to say, like nothing at all.
Spearfishing wetsuits: open cell and closed cell
Explainer · Last reviewed 2026-08-18
A spearfishing suit is warmth equipment, and warmth is dive time — which makes it the item that most decides how long a session can safely last, and the one beginners most often buy last.
Safety
Drowning and immersion — Can cause serious injury or death
The suit is the largest single contributor to a diver's buoyancy, and it loses buoyancy as it ages and as it compresses with depth. Weighting set for a new suit becomes over-weighting for the same suit two seasons later, and an over-weighted diver who blacks out does not float.
What reduces it: Re-check weighting whenever the suit is new, old, a different thickness, or joined by a hood — and have it checked in the water by somebody trained to check it rather than calculated from a formula. Weight for positive buoyancy at the surface.
Worse when:
- On deeper dives, where neoprene compression removes more buoyancy
- In fresh or brackish water, where less weight is needed than in the sea
Hypothermia — Can cause injury needing treatment
A suit that no longer seals — torn, aged, or the wrong thickness for the day — flushes continuously, and cold degrades a breath-hold diver's judgement before it produces symptoms they notice.
What reduces it: Suit for the water and the technique rather than for the air temperature, treat a tear in cold water as an end to the session, and stop at the first shiver.
Precautions that always apply here
- Never spearfish or freedive alone.
- Dive one up, one down: one diver down, one on the surface actively watching, every single dive.
Neoprene works by trapping gas bubbles that conduct heat poorly, and by holding a thin layer of water against the skin that the body warms once and then keeps.
OPEN CELL means the inner surface is raw neoprene rather than lined. It seals directly against skin, so almost no water circulates, which makes it markedly warmer than a lined suit of the same thickness. The costs are that it must be put on with lubricant — soapy water or a proprietary product — that it is fragile and tears easily, and that it is uncomfortable to remove.
CLOSED CELL or lined means a fabric layer inside. Easier to put on, more durable, and colder for the same thickness because more water moves.
MOST SPEARFISHING SUITS ARE TWO-PIECE — a high-waisted long john and a jacket with an attached hood — because that doubles the neoprene over the torso where core heat is lost and because the attached hood removes the neck gap that flushes cold water down a diver's back.
THICKNESS IS DECIDED BY WATER TEMPERATURE AND SESSION LENGTH, and the numbers differ enormously by region: 5–7 mm is ordinary in British, Irish and northern European water; 3 mm suits much of the Mediterranean summer; 1.5 mm or a rash vest suits tropical water.
And thickness cascades into weighting. A thicker suit is more buoyant, so it needs more lead — which is why the suit is bought before the weight belt is loaded, and why a change of suit means re-checking buoyancy in the water.
Cold is a safety variable, not a comfort one
The reason a suit belongs in a safety-first account of this discipline is that cold degrades judgement before it produces obvious symptoms.
A cold diver burns oxygen producing heat, which shortens the margin before hypoxia. A cold diver makes worse decisions about conditions, about surface intervals and about when to stop. And a cold diver's hands stop working, which matters when the thing that needs doing is releasing a weight belt or cutting a line.
That is why the honest guidance on thickness errs warm. A suit that is slightly too warm costs a little comfort on a hot day; a suit that is too thin costs dive time, judgement and eventually safety.
Hoods, gloves and socks are part of the same calculation. A substantial share of heat is lost through the head, and hands and feet are where the diver notices cold first and where loss of function has immediate consequences.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- RNLI water safety guidance: cold water shock and Float to Live — Royal National Lifeboat Institution (Water-safety or diver-training authority)Relied on for: Water safety guidance on cold water, its effects on the body and on decision-making.States this directlyPassage read and verified
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on cold as a factor in breath-hold diving incidents.States this directlyPassage read and verified
Camouflage, fit, and what actually matters
Spearfishing suits are sold in elaborate camouflage patterns, and the honest position is that fit matters far more.
A suit that fits badly flushes — water circulating through gaps at the neck, wrists and ankles carries heat away continuously, which is the mechanism a good seal exists to prevent. A poorly fitting 7 mm suit can be colder than a well-fitting 5 mm one.
On camouflage itself, the evidence is thin. What is established is that fish respond to silhouette, contrast and movement, and that colour is progressively lost with depth. A pattern that breaks up outline plausibly helps at close range in shallow water; the elaborate photographic patterns are a commercial development and FishingHQ does not claim a measured effect for them.
What is not in doubt is that a diver who is warm can stay still and stay long, and stillness is the thing that actually gets fish close.
The suit is part of the weighting system, and it changes with age
A wetsuit is normally chosen for warmth and then forgotten. It is also the largest single contributor to a diver's buoyancy, which makes it a safety component and makes 'which suit' a decision that has to be re-made whenever the suit changes.
NEOPRENE IS BUOYANT BECAUSE IT IS FULL OF GAS BUBBLES, and that is why a suited diver needs weight at all. Thickness therefore sets weighting: a seven-millimetre suit needs substantially more lead than a three, and switching between them without re-checking the weighting is switching between two different diving arrangements.
IT COMPRESSES WITH DEPTH, which is the part that makes freediving weighting genuinely different from anything else. A diver correctly weighted at the surface becomes progressively less buoyant as the suit compresses, and the deeper the dive the more pronounced it is. That is the mechanism behind the standard freediving rule of thumb — weight for positive buoyancy at the SURFACE with lungs empty — and behind FishingHQ's refusal to publish a weighting formula, because the correct answer depends on the suit, the person, the depth and the plan together.
AND IT LOSES BUOYANCY WITH AGE. Neoprene cells collapse over seasons of compression, so a two-year-old suit is less buoyant than the same suit new, and the weighting set when it was new is now over-weighting. Nobody re-checks this, and it is one of the few equipment problems that gets worse silently and continuously.
OPEN-CELL AGAINST CLOSED-CELL, IN THOSE TERMS. Open-cell interior neoprene seals against skin and is markedly warmer for a given thickness, which means a thinner and therefore less buoyant suit can be used for the same water — a real advantage that is usually described as a comfort one. The cost is fragility and the lubricated entry, and the tearing that follows getting either wrong. `suit-fin-and-personal-kit-failures` covers what a tear does and when it ends a session.
THE PRACTICAL RULE THIS ADDS UP TO: re-check weighting when the suit is new, when the suit is old, when the suit changes thickness, and when the water changes salinity. Have it checked in the water by somebody trained to check it, rather than calculated.
AND THE HOOD, GLOVES AND SOCKS ARE PART OF THE SAME SUM. Each adds warmth and buoyancy, and a diver who adds a hood for a winter session has changed the arrangement they weighted for.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Freediving safety practice: hypoxic blackout, its absence of warning symptoms, the ascent as the highest-risk phase, and the surface supervision that addresses it.States this directlyPassage read and verified
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Technical and sporting standards for underwater activities, including spearfishing conduct, technique convention and the safety expectations set by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated descriptions of established spearfishing practice and equipment convention, recorded as practitioner consensus rather than as scholarship.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where to go next
Where it matters
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Spearfishing
A membership assertion rather than a topical one: this record teaches the discipline or its equipment, so the discipline's mandatory safety posture applies to it.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing as a defined discipline with its own technical, equipment and safety standards, set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That the safety requirements of breath-hold diving apply across the discipline rather than to particular equipment or techniques within it.States this directlyPassage read and verified
Gear this affects
What these connections rest on (1)
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Suits, masks, fins and cutting tools
An explainer carrying a mechanism the equipment record depends on.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing practice, equipment convention and the safety expectations set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- BlueWater Hunting and Freediving — BlueWater Freedivers, Ventura, California, 1995 (Practitioner report)Relied on for: Spearfishing equipment and practice: gun, shaft, tip and rigging choice, and the handling of a shot fish, from a practitioner tradition distinct from the European one.States this directlyCitation checked — the work exists and is described correctly
Related reading
- Spearfishing in northern European watersA very thick suit is highly buoyant, needs more lead, and therefore raises the stakes of a weighting error — which is how cold becomes a safety issue rather than a comfort one.
- Suit tears, fin straps and personal kit that fails mid-sessionOpen-cell construction is what makes the suit warm and what makes it tear, which is the same property read twice.
- What a fish can see of you underwaterThe camouflage question answered from visual ecology rather than from marketing, including the trade against being seen by boats.
What these connections rest on (3)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Spearfishing in northern European waters
The equipment consequence of the region's governing condition.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Diving medicine guidance on breath-hold diving, cold exposure and the requirement for direct buddy supervision.States this directlyPassage read and verified
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Suit tears, fin straps and personal kit that fails mid-session
One record resolves a question the other raises and cannot answer alone.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing as a defined discipline with its own technical, equipment and safety standards, set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That the safety requirements of breath-hold diving apply across the discipline rather than to particular equipment or techniques within it.States this directlyPassage read and verified
Scientific evidence — 1 connection
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
What a fish can see of you underwater
The equipment record and the perceptual claim made for it.
- The Ecology of Vision — Clarendon Press, Oxford, 1979 (Scientific literature)Relied on for: Wavelength-dependent absorption and scattering in natural waters, and the contrast-limited nature of underwater vision.States this directlyCitation checked — the work exists and is described correctly
How this compares
- Reading underwater conditionsCold degrades judgement before it produces obvious symptoms, which makes thickness a safety variable.
- Weighting and buoyancy in spearfishingA thicker suit is more buoyant, so suit choice sets the weighting that follows from it.
- Wetsuits, fins and masks for spearfishingOpen-cell neoprene seals to skin and is warmer, more fragile and harder to put on.
What these connections rest on (3)
Authoritative guidance — 3 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Reading underwater conditions
Warmth is dive time and dive time is margin.
- RNLI water safety guidance: cold water shock and Float to Live — Royal National Lifeboat Institution (Water-safety or diver-training authority)Relied on for: Water safety guidance on cold water and its effects on the body and on judgement.States this directlyPassage read and verified
Weighting and buoyancy in spearfishing
The cascade from suit to weight to belt requirement.
- RNLI water safety guidance: cold water shock and Float to Live — Royal National Lifeboat Institution (Water-safety or diver-training authority)Relied on for: Water safety guidance on cold water and its effects on the body and on judgement.States this directlyPassage read and verified
Wetsuits, fins and masks for spearfishing
The equipment record and the thermal reasoning behind the choice.
- RNLI water safety guidance: cold water shock and Float to Live — Royal National Lifeboat Institution (Water-safety or diver-training authority)Relied on for: Water safety guidance on cold water and its effects on the body and on judgement.States this directlyPassage read and verified
Sources for this page
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Freediving equipment and thermal protection guidance.Background and mechanism onlyPassage read and verified
How FishingHQ labels evidence is explained in the evidence policy.