Interlocking Lead Bricks are tongue and grooved on four edges for easy stacking. They are generally used for High energy radiation shielding, but are available for ballast application as well.
Available sizes:1" x 4" x 12"1½" x 4" x 12"2" x 4" x 8"2½" x 4" x 12".  

Black is standard ( with other colors available)
2 Part Epoxy Paint 
100% Sealed for safe handling

This is new light-weight innovation that still provides all of the stability and protection for your lead caves with overall reduced weight. 
Available sizes: 3/4" x 4" x 12" and 1" x 4" x 12" Sizes
Both come with an outer plastic covering.

Available in multiple widths that come with or without grommets for a quick and easy protective curtain.