All breeds can be entered in their respective Breed Fur class.
Polish have commercial type fur, so your buck could also be entered in the Commercial Fur class.
Fur classes are divided into Colored (which refers to any rabbit with color other than white on the usable parts of the pelt, including broken) and White (which means white on all the usable parts of the pelt, i.e. pointed whites are included).
If your show offers premiums (awards) for fur, winnings in those classes will pay premiums. However, Fur classes do not count toward Grand Champion legs. Many people enter rabbits in Fur to gain a greater understanding of fur quality separate from the rabbit's overall type, and/or for bragging rights.