I wear some sort of kit nearly everyday, even for longer hours in the summer/hot months. I would suggest to anyone who does the same to go find themselves some good base layers that wick moisture off your body and does the job you need a base layer to do. I wore Nike Pro-Combat shirts nearly all last summer and will do the same this summer. If you are looking for a good shirt to wear for the hot months, you should try this.
If you are LE, Nike offers 30% off twice a year, 5/13/15 will be one of those days. Walk into a Nike store and show your ID/Badge and they'll knock 30% off.