Technical rain gear is your backcountry suit of armor: No matter how rainy, snowy, sleety, or windy it gets outside, the right waterproof jacket (and maybe pants, too) will keep you dry. The added protection is nice on a summer day-hike. For any higher-stakes activity, however, from winter excursions to multi-day treks to high-altitude missions, it’s downright essential where wet clothes can be uncomfortable at best and dangerous at worst.

Technical rain jackets (also called shells) are the ones suitable for just those types of trips—think backpacking, mountaineering, skiing, and climbing. There are scores of them on the market, using an alphabet soup of various technologies designed to be both waterproof and breathable. What they all aim to do: keep precipitation out while still allowing sweat vapor to escape, preventing you from getting wet from the inside. But what works for a 14er bid isn’t necessarily the best bet for hiking the Appalachian Trail. Here’s how to sort through the options.

In this article, you’ll learn:

• The technology behind different waterproof/breathable membranes
• The difference between 2-, 2.5-, and 3-layer jackets
• How to evaluate face fabrics for strength, stretch, and eco-friendliness
• What waterproof ratings mean
• How to compare different features

How Membranes Keep You Dry

There are several ways to add water resistance or waterproofness to a shell, but when it comes to technical gear, the best choice is a waterproof/breathable membrane. These delicate, ultrathin films contain countless minuscule pores—too small to allow water to pass through, but large enough to let body heat escape. They’re bonded to a face fabric (the outside of the jacket) for protection and durability, forming a layered material called a laminate. There are quite a few different membranes out there. 

The oldest and most recognizable is Gore-Tex, made from expanded polytetrafluoroethylene (ePTFE) and polyurethane that lets sweat from your skin diffuse through. Other brands offer air-permeable membranes, which allow air (but not water) to pass through from both the outside and inside, purportedly increasing breathability (NeoShell, eVent, The North Face’s Futurelight, Outdoor Research’s AscentShell). Yet another choice is a polyurethane (PU) membrane, which is hydrophilic (water loving) and therefore pulls moisture away from your skin. And two technologies—Columbia’s OutDry and Gore-Tex’s Shakedry—dispense with the face fabric and place the membrane itself on the outside of the jacket.

So which one is best? It depends: Any reputable waterproof/breathable membrane will keep water out. Breathability is the big X factor, and it depends a lot on other design choices in a particular garment, such as face fabric, fit, and pocket placement. And don’t forget: The one membrane that can completely keep up with body heat production at peak exertion has yet to be invented—in the worst conditions, you might feel swampy in even the most breathable fabrics available.

Why Layers Matter

When you’re reading the fine print on a rain shell, you’ll see a stat that reports the jacket’s number of layers. One of them is always the face fabric, and one is the membrane; where jackets differ is on the interior layer. Here’s what the three choices mean.

2-Layer 

This construction has a face fabric and a membrane, plus a mesh liner to protect the membrane. It’s the most affordable option, but typically not used in technical shells.

3-Layer

This option pairs the face fabric and membrane to an interior liner, which shields the membrane from abrasion and skin oils. Three-layer jackets are the most durable and often the most breathable—and the most expensive.

2.5-Layer

This “in-between” construction has a face fabric, membrane (or coating), and a raised pattern (the “half-layer”) on the interior to protect the membrane. These fabrics tend to be lightweight, but they’re less durable and often less breathable.

Consider the Face Fabric

Membranes are important, but a shell’s face fabric matters, too. It’s the jacket’s first line of defense against the elements, plus any trees or rocks you might scrape—and it also helps determine breathability and comfort. You might see the face fabric’s denier advertised. This is a measure of the density of a material’s fibers, and therefore, its strength. A lower denier (say, 20D) will be lighter and often more breathable, but more delicate; a higher denier (like 70D) will be burlier, but heavier and perhaps less breathable.

Another important factor: stretch. Generally, stretchy garments are more comfortable to wear because they move with you (particularly important for climbing or scrambling). Some face fabrics have four-way or two-way stretch, allowing for more freedom of movement; others don’t have much give.

The face fabric is also treated with a durable water repellent (DWR), which helps water bead up on the surface. Traditionally, brands have used PFC-based DWR, but these chemicals have been shown to wash out over time and build up in the environment. Brands are now working on eco-friendlier formulas, and some jackets offer PFC-free DWR. Though greener, these DWRs typically don’t last as long as their PFC counterparts, so you might have to re-treat the shell to restore its highest waterproofing.

What About Waterproof Ratings?

Another technical stat that shell brands like to tout is a measure of the fabric’s waterproofness as determined by a lab-administered water column test. A tube is placed over a swatch of fabric; the stat measures how many millimeters of water (and therefore, pressure) can be poured into the tube before the material starts leaking. A rating of 3,000 to 5,000 mm is considered waterproof against regular rain, but highly technical shells usually rate between 10K and 20K. Because it would take exceptionally high winds to get any rain through a 10K-rated shell, though, there’s little real-world difference in performance when you get into the higher ratings. 

What Features Do I Need?

Extras—such as pockets, pit zips, and an adjustable hood—make shells more comfortable and functional to wear, but they also tend to make them heavier. Think about your preferred balance of weight and features when comparing options.

Pockets

First, consider what kind and how many. Hand pockets are great for toting maps and snacks, as well as keeping your hands warm and dry in the rain. Chest pockets conveniently carry phones or GPS units, and internal pockets provide additional useful storage. Also check the size: Will your phone fit in that chest pocket? Finally, look at pocket placement: Will you still be able to access the hand pockets when you’re wearing a backpack hip belt or climbing harness?

Hood

Some cappers are more protective than others. Hoods that have adjustable toggles around the back of the head and/or around the face can be cinched down against nasty weather when necessary; the more adjustment points, the more control you’ll have. Some hoods are sized to fit over a helmet, which is important if you plan to wear it for climbing, skiing, or cycling. Also look at the brim: Some hoods sport substantial brims with bendable wire, which are great at keeping drips out of your eyes. 

Pit Zips & Mesh

Zipped vents under the arms (occasionally, you’ll also see these on the sides or back of a shell) open quickly and efficiently to dump body heat. Some shells also feature mesh-backed pockets you can open for extra venting, but keep in mind that you’ll risk losing anything stored inside them. 

Adjustable Cuffs & Hem

Cuffs that can be tightened with a Velcro tab let you firmly seal out wind and drips, and can be fine-tuned to fit over gloves. A cinchable hem also keeps cold drafts out when necessary, but loosens up for more airflow.

All articles are for general informational purposes.  Each individual’s needs, preferences, goals and abilities may vary.  Be sure to obtain all appropriate training, expert supervision and/or medical advice before engaging in strenuous or potentially hazardous activity.