The Science of Wet Weather Comfort

You’re in the local gear shop and you have one job: find a comfy but durable shell that will keep water out. But there are so many options—and the product hangtags seem to be written in code. Don’t worry. Here’s everything you need to know.
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You’re in the local gear shop and you have one job: find a comfy but durable shell that will keep water out. But there are so many options—and the product hangtags seem to be written in code. Don’t worry. Here’s everything you need to know.

How do you get wet when wearing a shell?

A common problem is that DWR wears out through abrasion, laundering, UV rays, or a combination of the three. When that happens, rain doesn’t bead up and roll off the same way; instead, it starts soaking into the outer fabric. That fabric eventually gets saturated, which blocks some or all of the perspiration vapor that’s coming through the inner membrane (or trying to come through) from escaping. When the vapor can’t escape, it condenses inside the jacket and makes you feel wet—which gives rise to the false conclusion that a jacket has lost its water-proofing. Most times it hasn’t.

My jacket is wet on the inside, but it’s not leaking.

What’s going on? The same way warm water vapor turns to droplets on the side of a cold glass, your sweat can condense into vapor inside your jacket. It’s called wetting out. It can happen when your jacket’s face fabric becomes overwhelmed and saturated — and moisture vapor has built up inside the jacket’s interior. Combat it by opening your jacket’s pit zips to vent excess heat — and wear layers that pull moisture away from your skin.

What’s a membrane?

It’s the waterproof breathable layer. In three-layer jackets, it’s sandwiched between your jacket’s outer fabric and interior lining, and the layers are bonded together to create the illusion of a single piece of fabric. In two-layer jackets, the face fabric is bonded with the membrane, which is protected by mesh or a taffeta fabric. A 2.5-layer jacket incorporates a print on the exposed membrane that adds the protection it needs, and is lighter weight and more packable.

What is "waterproof breathable?"

We know that might sound counter-intuitive, but trust us—it’s a thing, and you need it. Waterproof breathable jackets have pores that are too small for water to sneak through, but just big enough to let out water vapor from your sweat.

How does waterproof fabric work?

It depends. Some jackets pair a waterproof membrane beneath a more durable fabric coated in DWR. Others have waterproofing built right into the fibers of the yarn.

What's DWR?

Durable water repellent is a polymer that’s applied to the face fabric and helps your jacket shed water so you stay dry. In some jackets, it’s built right into the fabric’s yarns so it never has to be reapplied. In others, it can become compromised over time thanks to outside factors like dirt and bug spray. If that happens, you’ll have to re-treat the jacket with an after-market care product like Nikwax.

What does it mean to have "taped" seams?

Jacket seams are often sealed with waterproof tape that binds with the fabric to make sure no water sneaks in through the tiny holes sewing puts in the fabric.

What are PFCs?

Perfluorocarbons. They're man-made greenhouse gases that are released when making many common DWRs. They can stick around in our atmosphere for thousands of years. Look for PFC-free formulas to reduce your impact.

What is PVC?

Polyvinyl chloride, also known simply as vinyl, is a plastic synthetic often used for waterproof gear like thick rain coats and rain boots. It’s less breathable than lighter weight fabrics.

What’s air permeability?

It's the fabric's ability to allow air to pass through it. A jacket with higher air permeability can push heat and humidity out easier.

What's a hydrostatic head?

It’s a way to test waterproofing. A test tube of water is placed on the fabric and filled with water until the water pressure becomes too much that it seeps through it. The higher the number, the more waterproof the material is. Fabric is waterproof at 5,000mm. Most basic, entry-level jackets can withstand 10,000mm of water pressure. You’ll want a jacket with at least 20,000mm to combat heavy, persistent rain.

How can I keep my rain gear in good shape?

Protect it and keep it clean. Dirt and oil can degrade your gear’s waterproof capabilities. Wash and dry it after you go for a hike (make sure you’re using soap safe for the jacket, like tech washes specifically made for waterproof gear), and don’t leave it out in the sun for an extended period of time. If you have a super-thin rain jacket that relies on a membrane, avoid brushing up against sharp objects or rough surfaces like rock walls.

OK, so if my jacket leaks, is it ruined?

Not necessarily. Check for holes, and patch them with water-proof repair tape. If there are no holes, clean it with an after-market tech wash to revive your jacket’s waterproofing. Don’t forget to put it in the dryer; it helps bake the DWR onto the fabric face.

Stay dry in the wettest conditions with Marmot’s EVODry – rainwear reinvented at the molecular level.

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