Performance apparel is becoming much more popular among players of all ages and skill levels. Performance apparel is offered in two fits: compression and loose. Fit is a matter of preference, but in order to reap the true performance benefits of under apparel, the compression fit is the way to go. When you wear compression shorts/pants, shirts and socks, bloodflow is increased and your muscles recover more quickly. Most performance apparel is also hydrophobic, which means it will keep you cool and wick away sweat.
There's a difference between constriction and a healthy amount of muscle compression. If your compression apparel is too tight, your bloodflow will decrease and your muscles will grow weak more quickly because they will not receive enough oxygen to recover as you play/practice. Compression apparel should fit tightly and comfortably. So make sure that if you decide to wear compression shorts, pants, shirts, or socks, you get the proper size. Otherwise, you might as well just not wear it at all.
Loose-fitting performance apparel is moisture-wicking, breathable and comfortable, but it does not provide the benefits of muscle compression. It's a great choice for players who simply prefer this type of fit over the compression fit. Players have been wearing regular t-shirts and boxer briefs under their gear for years, so it's not like you'll be at a severe disadvantage if you choose to go this route, but you might want to try the compression fit before dismissing it because there are certainly a few benefits to wearing it.
Every manufacturer has been increasing the number of performance apparel options that they provide each year. Whether you prefer to wear Bauer, Reebok, Easton, Shock Doctor, or Under Armour, is totally up to you. But it's nice to know that you have options. Each of these manufacturers have performance apparel shirts, shorts, pants, and socks, as well as shorts and pants with integrated jocks and Velcro sock tabs. The all-in-one jock shorts and pants are very convenient and give you one or two fewer things to forget each time you pack your bag to head to the rink.
Like any other piece of equipment, hockey performance apparel gets pretty smelly if you don't wash it. Make sure you take a look at the tags to find the appropriate cleaning method. Most hockey performance apparel can be tossed into the washing machine, but make sure you take out your cup first, and like I said before, check the tags.