I worked at a high end mountaineering shop for many years and frequently fielded this question. People would come in, spend hundreds on a fancy waterproof/breathable jacket, and then return months later dissatisfied with the waterproofness. This is the clothing equivalent of someone bringing his Rover into the dealer to complain that it's not running well. "When did you last change the oil?" "Oh, I don't know, maybe 2 years ago?"
Many people dodn't understand how the garment technology works. In most waterproof/breathable (WPB) garments, there are multiple layers of fabric at work. The outer layer, what you see and touch, is typically nylon but can also be polyester. Below that, laminated to it, is the waterproof layer. This can be Gore-Tex, eVent, Conduit, there are countless branded versions of some kind of membrane that has holes in it big enough to let water vapor molecules (i.e. sweat) pass through but are too small to allow liquid water molecules to penetrate. Finally, on the inside of the jacket there is another layer that protects the membrane from getting abraded by your elbows, knees, zippers, etc. In lighter, newer jackets this protective layer will be pretty minimal.
A key piece in the correct functioning of WPB garments is something you can't see. At the factory these garments are treated with a spray that causes water to bead up and roll off. This is called a durable water-repellent finish (DWR). Why is this essential? The DWR keeps the face fabric (nylon) from absorbing water. Once the face fabric absorbs water, your water vapor can't pass through it so you start to feel wet. Meanwhile, the business layer- the waterproof membrane- continues to function as designed, but there's nowhere for the vapor to go because the outer layer of fabric is now a roadblock instead of a freeway.
Over time the DWR finish wears off- abrasion, dirt, oil, lots of things degrade it. Then the outer fabric of the jacket looks wet, the wearer feels wet, and the customer comes in to complain that his jacket is leaking.
There is a solution, but you need to have the appropriate expectation: you will never restore your garment to original factory condition. This annoys those people who spent $500 on a Canadian-made Arc'teryx jacket, but it's just as true for those jackets as it is for the $120 jackets you can buy at REI.
Solution:
1. Wash your garment. This gets rid of the dirt, oil, and other stuff that reduce the DWR effectiveness. But don't use detergent! Typical detergents contain surfactants, which not only pull the oil and dirt off your clothes but also pulls the DWR finish off your fancy jacket. Use a special soap typically called "tech wash", which is surfactant-free. A bottle of this will cost about $10-12 at an outdoor store and can wash 5-8 garments. To wash: close all zippers, fasten all velcro, turn garment inside-out, and run a couple rinse cycles after washing.
2. Re-treat. You can re-apply the DWR finish, but, as I said, it will not be as good as new. There are a couple kinds of treatments- wash-in and spray-on. I've had good luck with both. Again- close zippers, turn garment inside-out. It's not very helpful to re-treat a dirty garment, so take the extra step and make sure you wash it properly. A bottle of DWR treatment is also about $10-12 and can treat several garments.
3. Dry. Normal home dryer is fine, medium heat. Again- zippers closed, garment inside-out.
4. Iron. Sounds weird, but it works. Run a moderate iron over the outer fabric of the garment. This will (a) melt down the abraded strands of fabric that attract water, and (b) help ensure even, consistent coverage of the DWR finish.
Brands: they all work to some degree. The best performance I have personally seen is Revivex.
The key to optimal garment performance is like Rover maintenance: perform care and maintenance proactively so you don't end up with a major repair later. Do the 4-step care process at least once a year, preferably more often. And remember: the performance of the face fabric is not what determines the waterproofness of the garment- it's what affects the breathability. Just because it looks wet doesn't mean it's leaking. Change your oil every 3,000 miles, change your coolant every 24 months, and wash/retreat your jacket every year or less, and you'll have a longer and happier relationship with both.
