It is UHMW Plastic (ultra high molecular weight polyethylene)
It is the most popular type for "all around" use. It is very durable and will stand up to a lot of abuse.
Typically the best choice for temperatures above zero degrees Fahrenheit.
XH Plastic is typically in Black but can on occasion be White.
It is HDPE Plastic (high density polyethylene)
It is most popular for use in colder temperatures. It is soft and will scratch easily but performs great at sub-zero temperatures. It can be waxed for use in warmer temperatures.