By Eric Hagerman

They’re called rainforests for a reason. And although a jacket is the last thing you’ll want to don in the steamy jungle, you’ll need protection from the damp elements.

Barriers
Your first decision is whether you want a jacket with a laminate or a coating. A laminate is a membrane made from a material that lets water vapor out while preventing moisture from coming in; it's bonded to some fabric like nylon or polyester to make the shell. This is what most people think of as Gore-Tex, though there are a wide number of similar products from other manufacturers that work quite well. A coating is a chemical that is sprayed on, baked in, or otherwise affixed to the outside of the shell fabric. It's intended to have the same attributes, but because coatings can wear or wash off, they're generally less durable. Of course, they're also less expensive. Either way, make sure you get a jacket with sealed seams.

Vents
Underarm zippers, known typically as "pit zips," are crucial on any heavy-duty waterproof jacket. Despite the accepted terminology, waterproof-breathable shells, to be truly waterproof, are not nearly as breathable as you'll probably need. Thus the strategically placed zip: If you're overheating on a soggy slog through the rainforest, open them for immediate climate control. Some jackets have vents that run from under the arm down the length of your torso, a very clever way to achieve the same results.

Articulated Hood
A good hood is one that you don't notice, whether or not you're using it. The best designs include a draw cord at the back that pulls away extra material, cords at the sides that snug the hood around your face, and a strip of wire or plastic in the brim so that it doesn't flop into your field of view. Taken together, these features let the hood move naturally with your noggin. Also, you want the hood to roll up out of the way when not in use, but avoid ones that stuff into a zippered collar, which tends to feel like you're wearing a neck brace.

Zippers
YKK are the best, and yes, there is a difference. When you're trying on jackets, zip up with one hand, since that's likely what you'll be doing on the trail. If the slider repeatedly binds on the fabric, think twice about whether you want to own that particular jacket. Better designs use "upside down" zippers on exterior and interior pockets, meaning they open from the top down. Why? So your car keys and other essentials don't spill out when you open the pocket.

Eric Hagerman is senior editor at Outside magazine.