Ski shells are rated for their waterproofness and breathability. Generally speaking, the more waterproof a ski jacket, the less breathable it will be. If you are a backcountry skier and plan to do a lot of climbing, the breathability rating should be higher or equal to the waterproof rating. If you are skiing in a climate where the snow is very wet, waterproofing will be more important. Check and compare the waterproof/breathability ratings before you buy your ski jacket.

Water pressure in mm is the measure of waterproofness with a higher number indicating the garment is more waterproof. The moisture vapor transmission rate (MVTR,) measured in grams of water vapor per square meter per day, is the breathability rating. Higher MVTR indicates the garment is more breathable. For example, 15,000mm/10,000g would be more waterproof for wet winter alpine conditions while 5,000mm/8,000g would be more breathable for a backcountry shell.

Most skiers dress in three layers - a base layer, a thermal layer and a shell. There are two types of shells - hard shells and soft shells. Insulated jackets that combine the thermal layer and shell in one can come with either a hard shell or soft shell exterior. The primary differences between the two are:

The outer fabric of a hard shell is usually a woven nylon or polyester. A microporous polyurethane coating or laminate is applied to the inside of the shell fabric. The hard shell manufacturers either use the GORE-TEXR brand material or a one of their own design that carries their own brand name. Since the GORE-TEXR patent expired, many new materials have come on the market. Brand names for these coatings and laminates are GORE-TEXR, eVentT, HyventT, Omni-techT and others. The principal behind these materials are basically the same.

The idea behind these materials is to enhance the jacket fabric so that it is both waterproof and breathable. There are millions of tiny holes in the coatings and laminates which are small enough to keep liquid water from passing through, but are large enough to allow water vapor to escape. This allows water vapor from body heat, wet clothes or sweat to evaporate through the fabric while no water from the outside can get in.

Coatings are applied as a liquid. Laminates are a solid layer which is fused to the back of the fabric. Coatings and laminates act as a barrier to keep water droplets from penetrating the fabric while maintaining a microporous structure that allows much smaller water vapor molecules, generated from body heat, to escape to the outside, keeping you dry.

Different coating mixtures and laminate materials are used to provide the varying degrees of waterproofness and breathability levels available in different jackets. A less porous mixture creates a more waterproof ski jacket. Some laminates are also used as an interior finish, thereby eliminating the need for a separate lining.

The outside of the shell will be treated with a durable water resistant (or repellent) coating (DWR) to protect the outer material from water saturation. DWR is a liquid applied to the outside of the fabric. DWR keeps the fabric from `wetting out` or saturating the fabric from the exterior which will reduce the breathability of the coating or laminate. DWR acts like hair causing water to bead up and roll off the jacket. Beading makes the water molecules too big to fit through the pores in the fabric.

The DWR finish will carry its own rating level. For example: 80/20 DWR means that after 20 washings, the coating retains 80% of its original DWR quality. Teflon is a common component of DWR. Both hard shells and soft shells use DWR. DWR provides a stain resistant finish to the face of the fabric, allowing you to easily clean spots and spills with soap.

Some other fabric info: GORE-TEXR Hard shells come in 2 layer and 3 layer construction.

Soft shell ski jackets fabrics are both highly breathable and water resistant by design. Soft shells fabrics are known for their wind resistance as well. Many skiers prefer a soft shell ski jacket as the fabric is soft and stretchy. They don't make rustling and rubbing noise the way a hard shell does.

Soft shell fabrics range from the water resistant to the fully waterproof with DWR, like the Outdoor Research Mithril Stormshell Jacket pictured below.

Some softshells come in two fabrics with a laminated/more waterproof fabric across the shoulders and a more breathable fabric for the body - the shoulder fabric further eliminates the need for a hard shell, like the Cloudveil Rayzar Jacket shown below.

Soft shells are replacing fleece jackets and are well on their way to replacing hard shells in dryer climates. As an underlayer, soft shells are smooth and slip easily into sleeves, unlike fleece that tends to bunch up. Soft shells are quickly becoming the all around skier's choice in dryer areas like the Rockies. This year, insulated soft shells are on the market with all of the great features found in hard shell ski jackets - hood, powder skirt, pit zips, pockets etc.

Do you want a hard shell or a soft shell? Backcountry skiers like the soft shell for its breathability and stretch. Soft shells have become so good that many backcountry skiers merely keep a hard shell or down jacket in their pack just in case the weather becomes extreme - like a foul weather insurance policy. You can also get a hybrid hard shell/soft shell, like the Mountain Hardware Kramer Jacket below.