Overgrip goes over the existing racquet grip. As you use your racquet the grip will fill up with dirt and sweat and will feel slippery and loose it's adsorbtion. Many players wrap the grip with overgrip. Overgrip has excellent adsorbtion and gives a thin layer of padding. White overgrip has no pigments and can adsorb more. Also you can easily see when white is dirty and should be replaced. But many players prefer colored overgrip to enhance the look of their racquet.
Yonex Super Grap is a very popular brand. It is slightly tacky, adsorbant, and durable.
There are many brands of overgrip. Some are thin, some are adsorbant, some are soft, some are tacky, some are biodegrabeable. All brands are very good. Whichever you buy will work well; you can try several to see which you prefer.
