Our guide for how to choose the right tech for the moment.
When it's warm outside but raining, you want a jacket to protect you from the elements, but not suffocate you. Sure, you could use an umbrella, but that ties up one of your hands, drips when you get to your destination, and takes up space on crowded sidewalks or subways.
To know how to start looking for the right jacket for the weather of the moment, it helps to first understand the basics of how a jacket keeps precipitation out without keeping perspiration in.
At the heart of this type of gear is a membrane. You've likely heard of the most famous brand of waterproof, breathable membranes: Gore-Tex. (Other companies have their own takes on the tech; Outdoor Research makes “AscentShell,” for example.) The idea behind the porous membrane is that it can let water vapor molecules out—that's your sweat!—but not allow big fat water droplets through to your skin.
To protect that membrane from the rough world outside and the oily grime on your own skin, outdoor companies build jackets that have multiple layers. Typically, they'll sandwich the membrane between an outer textile and an inner one that faces your body. The outer textile will also have what's called a DWR, or durable water-repellent coating, on it, to make the raindrops bead up and roll off rather than sitting on the fabric and seeping through.
So when you hear about a three-layer rain jacket, those are the three basic elements. (Sometimes companies advertise jackets as being 2.5 layers, in which case the layer closest to your skin is not a full-blown piece of fabric. Instead, it's a matrix of material printed on the backside of the membrane. REI has a good explainer.)
In general, a very lightweight jacket is less durable—but more comfortable in the summer—than a heavy-duty one, which would hold up better under a heavy backpack during a serious expedition. One simple indicator of how robust the jacket is to check its actual weight, which will be measured in ounces. For example, a lightweight jacket could weigh just around 6 ounces, whereas a gnarly, heavyweight item could be over a pound.
The right fit, and pit zips
It doesn't matter how good your rain jacket is if it doesn't fit your body. A baggy jacket can create pockets of muggy air, called “microclimates,” between you and the garment. And if the fabric is all bunched up, it won't be able to let your sweat pass through it easily. A jacket with built-in stretch will let you buy a size that fits snugly but still give you a nice range of motion. Pick a jacket that will fit your body closely—with room for a thin insulating layer if you want to be able to wear it when it gets chillier out—without restricting your motion.
One other key detail to look for when shopping for a jacket is the pit zip: a zipper under each armpit that you can pull to create an opening to let your body breathe even better. When it's chilly or the weather is truly nasty, you can close them back up.
Just two layers
An extreme example of a lightweight, breathable rain jacket is a line that Gore-Tex makes calls Shakedry. Instead of sandwiching the membrane between two layers, the outer layer of the jacket is the membrane itself—there's no fabric covering it. It's just a two layer jacket: a membrane, then an inner textile against your body.
This is not the kind of jacket to buy and throw underneath a heavy backpack on a multi-day hike (the material might eventually wear out), nor is it a budget option. Instead, a jacket with Shakedry tech is intended for activities like running or biking. And while they're very lightweight, they carry a heavy price tag. Two garments that use Gore-Tex's Shakedry material are the Arc'teryx Norvan SL Hoody (for men or women), which costs $299 but weighs less than 4.5 ounces, and the North Face Hyperair trail jacket (for men or women), which is $250.
In brief: You're paying a premium price for a jacket that's very light and breathable, but likely less durable.
You don't need to shell out over $200 for a super-lightweight piece of gear. These are other popular options in the category:
REI has their own brand of gear, and their Co-op Essentials lightweight jackets come in at less than $100 and less than 9 ounces—see their men's and women's options. Their Drypoint GTX jacket is pricier, but newer.