Just because you are working hard, sweating, and putting everything you can into practice doesn't mean you should be uncomfortable doing so.  Get the comfiest practice jersey around, the Core 200 Series Jersey by Bauer.  The Core 200 features 100% breathable polyester, making this jersey very lightweight so it doesn't weigh you down, plus it keeps you nice and cool.  Get the most out of your jersey so you can get the most out of your practice.