Sheet updated September 2026
The O'Neill Psycho Tech 5/4+ Chest Zip is O'Neill's premier cold water fullsuit. It features 5 mm neoprene on the torso and 4 mm on the limbs. The Psycho Tech series showcases O'Neill's most flexible neoprene and their most watertight seams. It comes with a F.U.Z.E. chest zip, TechnoButter 3 neoprene, Air Firewall lining on the chest and back, and stitchless seams. O'Neill rates this fullsuit for water temperatures from 4 to 11 degrees Celsius. This specific fullsuit is a unique store item, available in size ST.
KEY INFORMATION
O'NEILL PSYCHO TECH 5/4+ CHEST ZIP - Men's extreme cold water fullsuit
What we like
- F.U.Z.E. Chest Zip: A chest entry system significantly reduces water ingress compared to a back zip. This design also keeps the back entirely flexible, as it's free from zips.
- TechnoButter 3 Neoprene: This is O'Neill's most elastic neoprene. It ensures that even a 5/4 fullsuit feels incredibly flexible, not like restrictive armor.
- Air Firewall Lining: Located on the chest and back, this lining traps air to retain body heat. It also dries quickly between sessions, keeping you warm and ready for your next ride.
- Stitchless Seams: The neoprene remains unpunctured with this design. An external weld combined with internal TB3X tape ensures the seam never becomes a point for water entry.
- Rated 4 to 11 Degrees Celsius: O'Neill provides this water temperature range, making it ideal for the entire Atlantic winter season.
- Top of the Range: The Psycho Tech series is where O'Neill incorporates its best materials, surpassing the Hyperfreak and Epic lines.
Available sizes
Included / Not included
✔️ Included: 1 O'Neill Psycho Tech 5/4+ Chest Zip fullsuit
✗ Not included: Hood, Boots, Gloves
DETAILED DESCRIPTION
What makes a Psycho Tech wetsuit stand out
O'Neill categorizes its wetsuits into distinct series: Epic for entry-level performance, Hyperfreak for lightweight flexibility, and Psycho Tech for superior warmth and durability. The Psycho Tech line features TechnoButter 3, the brand's most flexible neoprene, along with stitchless construction. This fullsuit is for long, demanding sessions in cold water, not just occasional use.
The F.U.Z.E. chest zip
The F.U.Z.E. system is O'Neill's exclusive chest zip design. Compared to a back zip, the chest opening significantly reduces the area where water can enter. Crucially, it leaves the back entirely in neoprene. This ensures maximum flexibility. While donning it might take a couple of tries to get the knack, it quickly becomes faster than a back zip.
Stitchless seams and Air Firewall
A wetsuit's warmth comes from two key factors: the neoprene itself and the seam construction. Here, the seams are not stitched, meaning the neoprene is never punctured. Instead, there's a fluid weld on the exterior and a TB3X tape glued on the interior. The Air Firewall lining on the chest and back adds a layer of trapped air precisely where your body generates its heat.
A unique piece, in ST
This product description refers to a store sample, available in size ST. For O'Neill, ST stands for S Tall: it's the fit of a size S, but designed for a taller body size/build. The brand's guide recommends it for riders between 183 to 188 cm tall and weighing 66 to 75 kg. If you fall within this range and have a slender body size/build, this is the perfect size for you. Only one is available.
SIZE GUIDE
| Size | Height (cm) | Weight (kg) | Chest (cm) | Waist size (cm) |
|---|---|---|---|---|
| ST | 183-188 | 66-75 | 95-99 | 75-79 |
TECHNICAL SPECIFICATIONS
| Specifications | |
|---|---|
| Type | Men's fullsuit, long sleeves and legs |
| Thickness | 5 mm on the torso, 4 mm on the limbs |
| Admission | F.U.Z.E. chest zip |
| Neoprene | TechnoButter 3 |
| Lining | Air Firewall on chest and back |
| Seams | Stitchless, external weld and internal TB3X tape |
| Advertised water temperature | 4 to 11 degrees |
| Series | Psycho Tech |
| Available size | ST |
| O'Neill reference | 5365 |
FAQ - O'NEILL PSYCHO TECH 5/4+ CHEST ZIP
This wetsuit is for riders who are in the water for long periods during winter. A 5/4 chest zip in this price range makes sense if you go out regularly between November and March. For just two or three winter sessions a year, an Epic or an Hyperfreak is enough.
O'Neill rates it for 4 to 11 degrees Celsius. On the Atlantic coast, this covers the entire cold season. Below 8 degrees, you will also need a hood and boots. Gloves are also necessary. These are not included.
Only one size is available here: ST. The O'Neill size guide higher on the page provides its measurements. A wetsuit must be tight when dry; otherwise, it will let water in. If you are unsure between two sizes, call us.
Rinse it with fresh water after each session. Turn it inside out and let it dry in the shade on a wide hanger. Never dry it in the sun, on a radiator, or folded wet in a bag. These are the fastest ways to ruin a wetsuit.
We are a Kite, wing, and Surf shop in Pornichet, on the Atlantic coast. We ride all year in water that drops below ten degrees in February. We wear winter wetsuits before selling them. If you have a question about sizing or cut, call us or visit the shop.
▶ Need advice?
GlissEvolution, 2c avenue du Gulfstream, 44380 Pornichet (Loire-Atlantique)
09 62 64 74 77 | WhatsApp: 07 83 28 39 94, Tuesday to Saturday, 10am-1pm / 3pm-7pm
Test center available by appointment
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