Nike Volleyball Bubble Kneepads
$20
Provide a lot of cushioning to protect your knees. This extra support can be helpful if you are a beginner or a younger player. If you are an older player or if you feel more comfortable diving and passing this amount of cushioning should not really be necessary. With proper technique you should not have to worry about banging up your knees so this much padding is excessive.
Pros: extra support
Cons: bulky, uncomfortable
Nike Volleyball Dri-FIT Skinny Kneepads
$18
My personal favorite. These are comfortable and durable. They easily lasted me through an entire season and at such a low price I never felt guilty buying a new pair for every season.
Pros: lightweight, very durable, come in multiple sizes
Cons: Only come in white

