How Neoprene Thickness Affects Your Spearfishing Dive

Neoprene thickness — measured in millimeters — controls how much insulation your wetsuit provides and how much it restricts your movement. The three most common thicknesses for spearfishing are 3mm, 5mm, and 7mm. Thicker neoprene keeps you warmer but makes you more buoyant and less flexible; thinner neoprene lets you move freely but offers less thermal protection. Your choice depends on water temperature, how long you plan to stay in the water, and how much mobility matters for your hunting style.

Neoprene works by trapping a thin layer of water between the suit and your skin. Your body warms that water, and the neoprene slows heat loss. Thicker material holds more water and provides better insulation, but it also compresses at depth, reducing its effectiveness the deeper you go. Most spearfishers choose based on the coldest water they regularly hunt in, then adjust with layering or different suits for warmer seasons.

Key Takeaways

  • 3mm neoprene suits are best for warm water (above 70°F) where you need mobility over warmth, such as shallow reef hunting or brief dives.
  • 5mm neoprene is the middle ground, offering reasonable warmth for temperate water (60–70°F) while keeping your range of motion acceptable for most spearfishing.
  • 7mm neoprene provides maximum insulation for cold water (below 60°F) but adds significant buoyancy and stiffness that requires weight adjustment and affects your ability to stay down.
  • Thickness affects buoyancy: thicker suits make you more positively buoyant, so you will need more weight on your belt to descend and stay neutral at depth.
  • Compression at depth reduces the insulating value of any neoprene, so a 7mm suit at 100 feet provides less warmth than at 30 feet.

3mm Neoprene: Warm Water and Shallow Hunting

A 3mm suit is the thinnest practical choice for spearfishing and works best in warm, shallow water where you are hunting for short periods. Water temperatures above 70°F — typical of tropical reefs, summer coastal dives, and shallow lagoons — are where 3mm excels. You stay warm enough for 30 to 60 minutes, depending on your metabolism and exact water temperature, and you retain nearly full range of motion in your shoulders, elbows, and knees.

The trade-off is minimal insulation. Below 70°F, a 3mm suit becomes uncomfortable within 20 to 30 minutes for most divers. You also get almost no thermal protection if you are hunting in winter or in deeper, colder water. A 3mm suit adds very little buoyancy — typically 2 to 4 pounds of positive buoyancy — so you will need minimal extra weight, which keeps your belt light and your weighting simple.

3mm is also the choice for hunters who prioritize speed and stealth. The thin material does not restrict your chest expansion, so you can take full breaths between dives. Your arms move without the drag of thicker neoprene, which matters if you are stalking fish in shallow water where a quick, smooth approach makes the difference.

5mm Neoprene: The Standard for Temperate Water

5mm neoprene is the most common thickness for spearfishing because it balances warmth and mobility across a wide range of conditions. Water between 60°F and 70°F — typical of spring and fall hunting, Mediterranean dives, and many temperate coasts — is where 5mm performs well. You can stay comfortable for 45 minutes to over an hour, and the suit remains flexible enough for normal hunting movements.

A 5mm suit adds 6 to 10 pounds of positive buoyancy, so you will need a modest amount of weight — usually 5 to 8 pounds depending on your body composition and the suit's exact construction. This is manageable on a standard weight belt and does not significantly change how you descend or maintain depth control. The thickness also provides real thermal protection: you stay warm enough for extended dives without the stiffness that comes with 7mm.

5mm is also a practical choice if you hunt in variable conditions. A single 5mm suit works reasonably well in water from 55°F to 75°F, so you can use it across seasons without buying multiple suits. Many spearfishers who hunt year-round in temperate regions own one good 5mm suit and add a thinner 3mm for summer or a thicker 7mm for winter rather than maintaining a full wardrobe.

7mm Neoprene: Cold Water Protection and Buoyancy Trade-offs

7mm neoprene is built for cold water below 60°F, where you need maximum insulation to stay comfortable for extended dives. Winter hunting, deep cold-water reefs, and northern or southern ocean locations all call for 7mm. The suit keeps you warm for 90 minutes or longer, even in water in the 50s, and provides genuine protection against hypothermia on long sessions.

The cost is significant buoyancy. A 7mm suit adds 12 to 18 pounds of positive buoyancy, which means you need substantially more weight to descend and stay neutral. This extra weight affects your weighting distribution, your descent speed, and your ability to stay down without active finning. Many spearfishers in cold water use 15 to 25 pounds of lead, compared to 5 to 10 pounds in a 5mm suit. That extra weight also tires you faster and makes recovery at the surface harder.

7mm also restricts movement more than thinner suits. Your chest feels compressed, your shoulders have less range, and your legs move with more effort. This matters less if you are hunting deep reefs where you are descending and holding position rather than chasing fish in shallow water. But if you hunt shallow kelp forests or rocky areas where mobility is critical, the stiffness of 7mm can work against you.

How Compression Changes Insulation at Depth

Neoprene loses effectiveness as you descend because water pressure compresses the gas bubbles inside the material. A 7mm suit at the surface might provide excellent warmth, but at 80 feet the neoprene is compressed to roughly half its thickness, and its insulating value drops significantly. This is why divers hunting deep cold water sometimes wear a 7mm suit plus a thin 3mm or 5mm layer underneath — the extra material compensates for compression.

This compression effect is one reason why thickness alone does not tell the whole story. A 7mm suit keeps you warm in 50°F water at 30 feet, but the same suit at 100 feet in the same water will feel noticeably colder because the neoprene has compressed. If you regularly hunt deep, you may need to go thicker than you would for shallow hunting in the same water temperature, or accept that you will get cold on longer dives.

Matching Thickness to Your Hunting Style and Water

Choose 3mm if you hunt warm, shallow water and prioritize mobility — tropical reefs, summer coastal dives, or brief sessions where you are in and out quickly. Choose 5mm if you hunt temperate water year-round or want a single suit that works across seasons. Choose 7mm if you regularly hunt cold water below 60°F or if you spend extended time underwater and need maximum thermal protection.

Your body also matters. Larger, more muscular divers generate more heat and can use thinner suits than smaller or leaner divers in the same water. Women and smaller-framed hunters often need to go one thickness thicker than larger hunters in the same conditions. If you are new to spearfishing, start with 5mm in your local water and adjust from there — you will quickly learn whether you run cold or warm.

Consider also what you hunt and where. Reef hunters who move constantly and stay shallow can get away with thinner neoprene. Deep-water hunters who descend and hold position benefit from thicker material and can tolerate the reduced mobility. Kelp forest hunters need flexibility, so they often prefer 5mm over 7mm even in cold water, accepting that they will get cold on very long dives rather than dealing with the stiffness of thicker neoprene.

Frequently Asked Questions

Do I need to add more weight if I switch from 5mm to 7mm?

Yes. A 7mm suit is roughly 6 to 8 pounds more buoyant than a 5mm suit, so you will need to add that much weight to your belt to maintain the same descent and depth control. Start by adding 5 pounds and adjust from there based on how you feel underwater.

Can I wear a 3mm suit in 60°F water?

You can, but you will get cold within 20 to 30 minutes. If you are hunting for short dives or brief sessions, 3mm is manageable. For anything longer, move to 5mm or accept that you will need to get out and warm up frequently.

Does a thicker suit make me float more at the surface?

Yes. Thicker neoprene is more buoyant, so a 7mm suit will float you higher at the surface than a 5mm suit. This makes recovery easier but means you need more weight to descend, which can make you sink faster if you are not careful with your weighting.

What happens to my 7mm suit's warmth if I dive to 100 feet?

The neoprene compresses under pressure, so its insulating value drops. A 7mm suit at 100 feet provides roughly the warmth of a 4mm or 5mm suit at the surface. If you regularly hunt deep cold water, consider going thicker or wearing a layered system.

Should I buy different thicknesses for different seasons?

If you hunt year-round in temperate water, one 5mm suit works across most seasons. If your water temperature swings from 75°F in summer to 50°F in winter, owning both a 3mm and a 7mm gives you better comfort and performance than trying to make one suit work for everything.