If Fixer is talking about a regular cotton T, that is not as cool as a Jersey made of 100% polyester. For some reason cotton fabrics do not work well when cycling, this has been known for years; it stays wet longer and when you come down hills the wetness can actually give you chill. All Jerseys made for sport use are made of either polyester or wool, polyester is the fabric of choice these days because it does have better wicking abiltity then cotton. The cheap $15 Walmart jersey I buy is 100% polyester and is just as effective as my $80 "high Tech" cycling jersey. I also have a wool jersey but when it gets over 90 degrees I don't think it's as cool as the polyester, but it won't stink after one ride (though I still wash it anyway) like the polyester's do. I find the short sleeve wool jersey to be more comfortable then the polyester when temps are from 50 to 85; but also long sleeve wool is more comfortable then Polyester in colder temps below 50. But wool is expensive (over $100), especially if you want to be able to machine wash it; so thats why I now buy the $15 Walmart 100% polyester jerseys.