For climbing at the gym, go for comfort. Loose and stretchy is good. Super-tight clothing is bad and will just restrict your movement. Take a spare T-shirt or another layer for afterwards.
For summer climbing, when it comes to T-shirts for rock climbing, choose something breathable and sweat-wicking. Maybe you already own a T-shirt or some top from another sport that’s suitable. Go for something flexible, but not too baggy so that it doesn’t get in the way. Some fabrics also come with UV protection.
Why not consider responsibly-produced fabrics? We all have a responsibility to minimize the impact of the clothing that we make and wear and to improve the lives of the people involved in its production.
Wild Country is a member of the Fair Wear Foundation for this very reason. The independent non-profit organisation works to improve labour conditions in the clothing industry. We also recommend more sustainable options, such as organic cotton or hemp and Tencel™ blends.