The art and science of staying dry

The one place you don’t want to be making decisions about how to keep the rain off you is when the first drops are falling from the sky.  I can’t tell you, though, how many times I was in exactly this position before I finally started taking steps to keep dry.  Beating the rain is all in the planning, and it starts with what you choose to wear even when there’s not a cloud in the sky.  Staying dry means thinking about your wardrobe from the ground up.
I used to be an “all cotton” kind of guy.  Cotton t-shirts, overshirts, socks, blue jeans and underwear.  This was comfortable when I spent a lot of my time indoors, but it meant, without fail, that I was absolutely miserable in the rain.  Cotton is a great fabric, but it absorbs water and holds on to it, locking it into the weave.  Whether this moisture is rain or sweat, cotton will not let it go and will not dry out for hours.  If this weren’t bad enough, once cotton soaks through, it also fails to hold warmth.  What this means is that wet cotton clothes will keep you both wet and cold, neither of which is ideal.  On top of this is the clincher, because wet cotton also binds and chafes.  This means that long-term walking in cotton underwear is a recipe for disaster, in sunshine and especially in the rain.  Rethinking my rain clothing involved rethinking the fabrics I wear on a regular basis.
Here are some qualities you should look for in good rain clothing.  First off, let’s get some some terminology in place.
Moisture wicking: These fabrics pull wetness away from the skin and transport it through to the outer layer.  These types of fabrics are excellent to use in base layers (those closest to the body).  However, read the labels carefully.  Some articles of clothing are labeled as moisture wicking but contain cotton and other slow-drying fibers.  Therefore, you need to match moisture wicking with clothes that are
Quick drying: As the label says, these fabrics shed moisture very quickly.  A variety of blends have this quality, including some containing cotton.  Some achieve the quick-drying quality through chemical treatments, others through a specific weave, or a combination of the two.
The secret to good clothing is to match and layer fabrics with an eye to transporting moisture away from the body comfortably and getting it to the surface of the clothing where it will evaporate quickly.  On dry days this allows you to stay active and comfortable with maximum movement and minimum discomfort or chafing.
Start with a good core.  For example, I switched out my cotton boxers and undershirts for a set of underwear made of synthetic materials that wicks moisture much more effectively.  For a while I was using Champion C9 boxer-briefs in combination with C9 all-polyester t-shirts.  The briefs were quick drying, but were not really well-designed for comfort.  The t-shirts, however, worked great and are still part of my wardrobe.
An enthusiastic salesperson at REI told me about ExOfficio Boxer Briefs.  I bought a pair, thinking that I would use them mainly during travel.  However, after trying them on a few trips, I liked them so much I ended up replacing my regular day-to-day cotton underwear with them.  The final touch was to start wearing thin, moisture wicking socks underneath my regular socks.  So this combination is my basic layer for day-to-day wear.  On cold days, I’ll add some thermal leggings as well.
Once the base layer is established, the key is to build on it according to the conditions.  I have a variety of shirts and pants that each do a good job of drying quickly and keeping me warm.  The key is that, day to day, as I am active and move and sweat, the combination keeps me dry and comfortable.  The clothing is so good, in fact, that a few weeks I was caught in a full-on torrential downpour, and managed to get through the day without too much discomfort.  I was damp, but I wasn’t soaked.
The final key to staying dry is planning an outer layer that can be put on over your daytime clothing.  For me, I have been very pleased with a combination coat and pant set from Helly Hansen.  While this rain gear wouldn’t do for all-day wear (if you’re looking for that sort of thing, you’ll want to try some Gore-Tex products), they are the best I have found for keeping the rain absolutely repelled.
Even if your strategy differs from mine, it all comes down to good planning.  The closer you come to your rain wear being a part of your every day wear, the more effective it will be.