So you finally saved up enough vacation days and frequent flyer miles to take that trip to the tropics to indulge in a week of dive-eat-dive-sleep-dive-dive-dive. Nothing's going to stop you from loading up on bottom time—except maybe hypothermia from diving too long in that worn-out wetsuit you've been meaning to replace.

While a lot may have changed in the world of wetsuits since you plunked down those eighty bucks on that old neoprene soldier in your closet, a 3mm fullsuit still tends to be standard fare for diving low-70s to 80-degree water. And since warm water tends to be where most divers flock when they get the chance to take a dive trip, it's arguably the most popular type of wetsuit being sold today. But while at first glance all 3mm wetsuits may look pretty much the same, there are many differences in material, seam construction and sealing methods that play a role in maintaining comfort and warmth, which translates into more dive time, which, of course, is what it's all about.

Wetsuit Basics

As soon as you hit the water the clock starts ticking toward hypothermia, even when diving in the tropics. The goal of a wetsuit is to delay this event by reducing the heat loss caused by the water that comes in contact with your skin, while at the same time providing a level of comfort and flexibility. How well a wetsuit accomplishes this depends on how well its components work together to create an efficient thermal wrap.

Materials: On each side of a wetsuit's neoprene rubber there is a layer of material, usually nylon. The purpose of the outer layer is to provide some protection for the neoprene, while the inner layer, or lining, goes more for comfort. Some suits use no inner lining, opting instead for a smooth-skin interior. This approach offers better warmth capabilities because the whole suit seals against your skin, minimizing or even eliminating water flow, which is a key ingredient to an effective wetsuit. The downside: wetsuits with smooth-skin interiors, with some notable exceptions, tend to be more difficult to don and doff, especially when the suit is already wet, and the inside of the suit is more prone to damage.

The big push in recent years has been toward stretchier neoprene to increase comfort and flexibility. A stretchier suit is easier to climb into, is comfortable and is able to maintain a snug fit by conforming to all your curves. Of course, stretchier neoprene compresses more at depth than denser, stiffer, standard-stretch neoprene, reducing its insulation capabilities. Because of this, some wetsuit manufacturers have chosen to stay with more traditional compression-resistant neoprene for its thermal advantages, which is then cut into a series of anatomically shaped panels and sewn together to address the flexibility issue.

Seams: Seams of 3mm wetsuits are usually flat-stitched (also called flat-seam or flat-lock stitching) or glued and blind-stitched. Flat-stitching is less costly and offers a softer seam that's more comfortable against bare skin. However, a flat-stitching needle goes completely through the neoprene and nylon laminate, resulting in a thousand thread holes and leaky seams.

Glued and blind-stitching involves first gluing the suit's neoprene panels with two or three coats of neoprene cement. This makes the seams waterproof. The second step is sewing the seams together to prevent them from pulling apart. This is done with a "blind-stitch," where the needle penetrates only the top layer of the material, never going all the way through the neoprene. Glued-and-Taped is a variation of this method, where flexible bonding tape is applied with heat and pressure over the glued seam, eliminating the need for any stitching at all.

Seals: A wetsuit's ability to keep you warm will be compromised if water can flow freely in and out of the suit. Of course, these are "wet" suits, and some water is expected to seep in, you just want to keep it to a minimum, and you want to definitely avoid any type of water flow that continually displaces the warm water that's already in the suit with new cold water that immediately starts sucking more heat from your body. Water entry points, in order of importance, are the neck, the wrists, and the ankles. Some manufacturers put serious sealing systems on each of these entry points. Others focus on the neck while forgoing seals on wrists or ankles or sometimes both. The ideal way to minimize water intrusion, of course, is to have some type of sealing system at each of these entry points.

There are a number of types of seals used on modern 3mm wetsuits. Starting with the most effective, they are:

• Rolled smooth-skin seals. You often find this type of seal on dry suits but we've started seeing it on wetsuits too. It's a long cuff of neoprene with smooth skin on the outside that's been rolled or folded under so the smooth-skin seals against your bare skin.
• Standard smooth-skin seals. This is a length of smooth-skin material that runs up the wrists and ankles and/or around the neck. Sealing against bare skin, it provides an excellent water block—if the seal isn't broken. Generally, the farther the area of smooth-skin reaches up onto forearms and calves the better the chances that the seal won't be broken. This happens often on ankle seals, where the area of smooth-skin isn't quite long enough to reach above the top edge of a diver's tucked-in booties. However, if you're not wearing booties, which is quite common in tropical waters, this is not a problem.
• O-ring seals. This is an elastic smooth-skin ring seal located right at the hem of the wrist or ankle cuff. It's a simple design that doesn't get in the way when donning or doffing the suit. However, such a narrow ring of smooth-skin against bare skin creates a seal that is very easy to break. On some sinewy divers, protruding veins on the inner wrist is all it takes to break the seal and start water flowing.

Zippers: The zipper creates the largest opening of a wetsuit, so you can be sure that water will try to gain entry here. To combat this, most suits are equipped with a zipper underflap that lies between your bare back and the zipper track to help block water flow as well as provide some cushioned comfort. Some suits take it a step farther by using one or two sections of smooth-skin neoprene on one or both sides of the track that seal against the underflap and/or each other. Some suits take another approach by using zippers with overlapping teeth designed to reduce water seepage. The G-Lock zipper is a popular example of this type of zipper.

Time to Test

The 14 brand-new 3mm wonders sent in for this year's round-up got a rigorous working-over in the ScubaLab shop. We stretched the arms, pulled the legs, tugged at zippers. We turned them inside out, took note of the finish work and attention to detail. Then we hauled them down to our test pool where 75-degree water awaited us—well within the operational range of a 3mm wetsuit, yet just cool enough to easily feel the leaks.

ScubaLab staff, staged on the pool deck, donned each suit, checking to see how easy it was to pull on and self-zip. Then we went through a series of squats, body bends and arm reaches to assess each suit's comfort and range of motion. Checking to see that all seals and closures were snug, we then slowly entered the water, taking note where we felt leaks, i.e. through the seams, or at zipper, neck, wrist and ankles. Once fully-immersed, we checked for water entry at the ankles and wrists during feet-first descents. Then we shifted into standard swimming mode and checked for water scooping at the neck. Finally, using the same test diver to assure consistency, we performed a buoyancy check to give us a general idea of each suit's relative inherent buoyancy.

Find Your Fit

Finding a wetsuit that fits you like a second skin is 90 percent of the battle. Seals, seams, zipper … none of this matters if the wetsuit doesn't fit. Gaps in your armpits and spaces between your legs, behind your knees or in the curvature of your spine are just waiting to fill up and pump cold water around the inside of your suit, literally sucking the heat from your core.

A properly fitting suit encompasses your body with no gaps or spaces. Unfortunately, finding such a fit can be easier said than done. Everybody has a unique shape, and every manufacturer's definition of small, medium and large seems to be different. Some suits tend to be designed for muscular divers, others fit lean divers better. Some manufactures offer a dizzying array of sizes, others offer only the basics. Bottom line: To get a snug-fitting suit, you're going to have to work for it. That means trying on as many suits as you can. Find a manufacturer who caters to your body shape and who hopefully offers the suit you like in lots of sizes, then try them all on until you find the right size and the perfect fit.

By wearing a snug-fitting suit with no gaps or spaces, you'll burn less energy and stay warm longer. So keep looking until you find the suit that feels like it was made for you. And if you just can't find a stock suit that will do the job, many manufacturers are willing to custom cut a suit to match your unique measurements.

General Test Observations

• Glued and blind-stitched (G&BS;) seams are almost in a whole different category from flat-stitch seams because, simply, flat-stitch seams leak and G&BS; seams don't. Flat-stitched suits used to be less expensive than G&BS; suits, although that's not so much the case anymore. However, when it comes to diving in warm water, many divers don't mind—or actually prefer—to have their suits leak because it feels good and they aren't going to be the water long enough to get chilled anyway. Bottom line: for maximum warmth you want minimum water leakage, and all other wetsuit components being equal, that means a G&BS; suit. Note: of the 14 suits in this review, all but four use G&BS; seams.
• The neck seal is the most important seal in a 3mm suit. A good snug fit will keep the collar from scooping water and flushing your suit as you swim. While a smooth-skin seal is always preferred, we found some suits with nylon necks worked well simply because they had an adjustable collar that could be cinched up snug.
• Having zippers in wrist and ankle cuffs is generally considered to be an asset when it comes to donning and doffing a wetsuit. This is especially true with thick 7mm suits, where having zippers can make the difference between really difficult, and relatively easy, entries and exits. However, the contrast is much less stark with thinner 3mm wetsuits, especially 3mm high-stretch wetsuits which are generally very easy to don and doff without zippers, and only marginally easier with zippers. Bottom line: Zippered wrist and ankle cuffs almost always leak more than regular cuffs, so you end up with all the downsides of a zippered cuff, without needing what little upside it offers. Of the 14 suits in this review, four come with zippered cuffs on either wrists, ankles or both.
• Zipping up a back entry suit can be tough sometimes, due to the slider getting snagged in the zipper flap. A loop of webbing at the base of the zipper gives you something to pull against which helps. About half of the suits in this review had such loops.

How a Wetsuit Works

Wetsuits are made with neoprene rubber, a closed-cell foam that traps millions of tiny gas bubbles within its structure. Unlike open-cell foam (i.e. a sponge), water won't saturate neoprene, but the gas bubbles tend to give the material a lot of inherent buoyancy. When you climb into a wetsuit your 98.6-°F body temperature warms the gas bubbles in the neoprene, which act as insulation. This, combined with a snug, sealed fit that minimizes the amount of water that enters the suit and flows across your bare skin, is what keeps your body heat from escaping into the watery environment.

In order for a wetsuit to do its job it has to 1) be of a material thickness that suits the temperature of the water you're diving in, 2) it has to have seams, seals and zippers that minimize water intrusion, and 3) it has to fit. The truth is, no one suit will deliver the same thermal performance for all divers. There are simply too many variables that need to be factored in, like body size, body shape, body fat, etc. So when you hear some "expert" claim that one particular model of suit is warmer than another, what he's really saying is that it's warmer for him. You can't count on this being true for you. But what you can count on are a number of design and construction methods that make the difference between merely an okay wetsuit and a veritable top gun in thermal protection. Find a suit with all the right stuff, that also fits like a glove, and you will have found wetsuit nirvana.