Sweat keeps you cool because when water evaporates from a surface, it lowers the temperature of that surface. By drawing the sweat from your skin, these shirts increase the rate at which this process can happen, thereby making your natural heat regulation capabilities more effective. Thus, when you get a little warm, you sweat a little bit, the shirt amplifies the process and you cool down before you even know that you're sweating. When it's cool outside you stop sweating and then this shirt works like any other piece of clothing to keep you warm. In the words of Bill Nye, SCIENCE RULES.I especially love these shirts because they're low friction without being too slippery. Thus I can move around freely while rock climbing without feeling like I'm wearing a silk shirt from a 1980s disco.The only problem is that because this is a synthetic fiber, bacteria love it. Thus, you wear this while sweating and you instantly stink. The smell washes out easy enough, but if you like to get multiples wears out of a shirt before washing it, you should probably go with a wool-based or antimicrobial-treated shirt instead.

Sizing: I'm 6'1", 185 pounds and the medium is loose-fitting without being baggy.

As someone that tends to heat up quickly during physical activity, I was looking for a light spring jacket that would cut the chill when I left my apartment in the morning, but not cook me as I walked to work. This does the job perfectly. It's kept me warm down to 40 degrees (I haven't tried it in anything colder) and never ever leaves me damp. Put a hard shell over it, and you can handle almost any weather.

The fit is slim in the forearms which is odd at first, but I quickly got used to it. I'm 6'1" 185 lbs and the Large is a loose but good fit around my torso. The arms are long, but that's to be expected in a monkey-thumbed jacket.

I highly recommend it both as a light spring jacket and a super-warm midlayer.

These are the best shoes for a beginning climber looking to beef up their strength and technique in a gym before head out to their local crag. Science friction rubber is super-sticky, but a bit soft, so while they will last you a long time indoors (I've had mine 15 months and they are still going strong), they will get destroyed during outdoor climbing. If you buy them a bit tight so that your big toe is forced into a slight angle, the leather will strength out nicely to give you good solid toes. However, be very careful and err on the side of looseness, because it's not worth getting overly tight shoes if it gives you permanent nerve damage in your feet.

My advice is to buy a pair of these to start off your climbing career and then buying a second pair of La Sportivas or FiveTens for their more durable rubber when you move to outdoor climbing. That way you can still get plenty of use out of your Mad Rocks in the gym.