Road season is about to start here and I think that it is time I stopped using my cotton singlets as an undershirt and start using something more specific for cycling (and racing in particular). What is the best material for me to get?
Under Armour makes a line of Heat Gear shirts that are quite good in the summer; they're so light, they feel almost like you're wearing nothing at all. (I saw two sorts on the racks, and the shirts labeled "green" feel like they're made of a softer and more comfortable fabric. (I got them in yellow.)
They're polyester, so they wick well.
The short-sleeve shirts are inexpensive; the mens' tee-shirts go for about $25. The ladies' shirts go for significantly more, my wife just got the mens' shirts and they're fine for her.
My favourite base layers are Merino wool, in particular from Rapha. They are seriously not cheap, but they are definitely worth it. Very warm in winter with the long sleeve, but surprisingly cooling in the summer with the short/no sleeve.
They aren't cheap but you can normally find some online retailer (especially in the US) doing a deal.
Edit. apparently I'm a cheapskate! Expect to pay $10-15 for a short sleeve shirt. If you buy these brand names they will lost for many years. Only draw back is that the stuff does get smelly. Modern low temperature detergents don't kill the bugs - so if you are an extra smelly cyclist you have to soak them in bleach / bicarb / special running gear smell-killer occasionally.
If you take a look at the fabric care labels on these base layer products, it often states that the fabric is 100% polyester and sometimes a blend of polyester and spandex. However, for cycling (sports) gear the material is technically called microfiber. "The most common types of microfibers are made from polyesters." The key benefit of microfibers is that the material wicks moisture (sweat) away from the body, keeping the wearer cool and dry. (Unlike cotton which will keep you wet and clammy.)
When selecting, I look for labels specifying a base layer for warm weather. After that, for my personal tastes, I want the fabric to be soft, non-itchy, and form fitting. At this point I currently have Craft and Gore products for cycling since they meet my criteria. There are other brands of base layers, for example Nike calls it's base layer fabrics, "Dry-FIT".
Here's a link to a fabric library on BicycleApparel.com. As you can see there are quite a few proprietary names for polyester!
I wear something like this Gore Bike Wear Baselayer Shirt:
although I'm fairly sure I didn't pay anywhere near £30 for it. But I have had it for a few years now and it may be a completely inferior model to the one shown.
I like it because it acts as a wicking layer and a windproof layer, getting rid of my sweat and stopping the lovely subarctic winds which whistle down from the West Pennine Moors from making it chill next to my skin (and that's in the summer).
I live in Texas so this undershirt concept confuses me. Why would you wear more than 1 shirt?
Pearl Izumi Quest Sleeveless Jersey is my favorite on a hot day. http://www.pearlizumi.com/publish/content/pi_2010/us/en/index/products/men/ride/apparel/jerseys.-productCode-11121108.html#3DP