MTS™ (Moisture Transport System)

Your fabric drysuit, whether breathable or non-breathable, keeps you dry by preventing the outside water from intruding when you are immersed. The layer of air that is encapsulated inside the drysuit is warmed by your body heat. The undergarments that you wear inside your drysuit hold the air and prevent the outside water from squeezing the drysuit fabric against your skin, thus creating the thermal insulation.

The more you move around and exert yourself, the more heat your body will generate, keeping you warmer. At some point, the activities you do will cause your body to overheat, and you will sweat. When you sweat, the water molecules on your skin evaporate, becoming water vapor. This allows your body to cool down and be comfortable. However, when these water vapor molecules leave your body, they will soon cool down and condense back into liquid water. If the resulting liquid water remains in contact with your skin, you will quickly feel clammy and become chilled.

Each fabric drysuit user needs to manage potential moisture build up inside the drysuit by transporting the water vapor away from your body, to the outside of your undergarments. This transportation of moisture away from your body, through your undergarments, is commonly called "wicking".

If your drysuit fabric is "breathable", the water vapor will be transported from your undergarments, through the fabric, out to the outside "face" of the fabric, where it will evaporate.

If your fabric drysuit is non-breathable, this water vapor will not be transported through the drysuit fabric, but will condense on the inside of the fabric of the drysuit. You will still feel warmer and more comfortable, even though the condensed water is not "breathing" out through the drysuit fabric, because the water vapor is not condensing on your skin.

All of your undergarment(s) should be made from fabrics that are consistent with this Moisture Transport System. Most synthetic fabrics, polyester, nylon, and polypropylene, do not absorb water vapor, and do facilitate Moisture Transportation. Do not wear any cotton or wool layers. These fabrics, especially cotton, while effective in other uses, will absorb and hold water, preventing proper moisture transportation.

Polyester fabrics are comfortable, are easy care, have reduced odor contamination, and are very effective at moisture transportation. They are preferred as the wicking thermal insulation layers.

Select your undergarments to meet the thermal protection you will need, considering the cold and water exposure conditions, your metabolic output, how long you will be exposed, the amount of exertion you will do, and any other relevant factors. Your undergarments should conform as closely as practical to your body, to reduce any unwanted buoyancy and bulk.

Choose and layer your undergarments and accessories to create your own thermal protection systems, and you will stay warm and dry in all water immersion activities, from surface water use, to warm water diving, to ice diving!


Polartec® PowerStretch® Fleece

Fabric drysuits do not stretch. Your freedom of movement comes from our Freedom Cut™ drysuit design combined with undergarments that stretch and minimize bulk. Wearing bulky undergarments inside your drysuit will restrict your physical movements, and increase the friction of moving through the water or having the water move past you.

OS Systems makes a range of four way stretch fleece undergarments which can be chosen and layered to meet individual usages. These are made from Polartec PowerStretch Fleece, a double sided fleece that stretches at least 100% in all directions. These undergarments are designed to fit your body relatively closely, but stretch easily as you move, minimizing bulk and resistance. No other fleece stretches like Polartec PowerStretch Fleece

OS Systems makes its 4-way stretch fleece undergarments in both single and double layer versions. Except for the full body jumpsuits, the photos of the single and the double layer garments look exactly the same.

DU-SV – PowerStretch Fleece Vest, single layer
DU-SV2 – PowerStretch Fleece Vest, double layer

DU-ST – PowerStretch Fleece Long Sleeve Top, single layer
DU-ST2 – PowerStretch Fleece Long Sleeve Top, double layer

DU-SP – PowerStretch Fleece Pants, single layer
DU-SP2 – PowerStretch Fleece Pants, double layer

DU-SJ – PowerStretch Fleece Jumpsuit, single layer, with dropseat
DU-SJ2 – PowerStretch Fleece Jumpsuit, double layer, no dropseat.

DU-SS2 – PowerStretch Fleece Socks, double layer.

All of these PowerStretch undergarments can be layered with each other, or under the DU-NJ, Nylon Jumpsuit shown elsewhere in this undergarment section.

OS Systems offers the "Best Deal System" package additions which include the DU-SJ and the DU-NJ as our most preferred combination for diving drysuits and for Stream Count drysuits. Combine these two undergarments with an additional Vest, Top, or pants; or, upgrade from the DU-SJ to a DU-SJ2 for additional thermal protection.