5% borated polyethylene is a product typically used in the medical field to shield neutrons.  Made from UHMWPE with 5% boron content by weight, this material provides exceptional durability over a wide temperature range.
Borated polyethylene is available from Radiation Protection Products in standard-sized sheets (48" x 96" x 1"), as well as in blocks, slabs, and custom-size sheets. 

ADVANTAGES
Lower cost than lead
Lighter weight than lead
Replaces lead in nuclear shielding applications
Standard is 5% boron by weight – UHMWPE base material