FireDefender® Mineral Core material fills most of the space in the interior of a door. It is relatively light in density at approximately 32 pounds per cubic foot. It has excellent thermal properties and through-bolting is allowed, but it is not intended to provide screw-holding capabilities. FireDefender® mineral cores are made of a proprietary mix of various minerals, fiberglass, and inert binders. They are available in a variety of thicknesses ranging from 1.500" - 2.000" (38mm - 51mm) and in various sizes up to a maximum of 34-1/2" x 82" (876mm x 2083mm). The mineral core is easily sawn with ordinary woodworking equipment and can be pieced together to make doors as large as four feet wide and ten feet tall. Georgia-Pacific mineral core is also approved for use in temperature rise applications in wood fire doors.