Lightweight, reduced density fire rated gypsum panels

A fire resistant gypsum panel comprising a gypsum core disposed between two cover sheets, the gypsum core comprising a crystalline matrix of set gypsum and high expansion particles having a volume expansion of about 300% or more of their original volume after being heated for about one hour at about 1560° F. distributed within the gypsum core;

• the panel having a panel density of about 40 pounds per cubic foot or less and a core hardness of at least about 11 pounds, and the gypsum core and the high expansion particles effective to provide the panel with a High Temperature Shrinkage (S) of about 10% or less and a ratio of High Temperature Thickness Expansion to High Temperature Shrinkage (TE)/S of about 0.2 or more.

A fire-resistant gypsum panel comprising a gypsum core disposed between two cover sheets, the set gypsum core comprising a crystalline matrix of set gypsum and expandable particles distributed in the crystalline gypsum matrix, the set gypsum core having a density of about 40 pounds per cubic foot or less and a core hardness of at least about 11 pounds, the panel having a nominal panel thickness of about ⅝-inch, the expandable particles having a first unexpanded phase and a second expanded phase when heated, the panel effective to inhibit the transmission of heat through an assembly of said panels prepared and heated pursuant to the procedures of UL U419, where surfaces of the panels on one side of the assembly are exposed to a heat source and surfaces of the panels on the opposite, unheated side of the assembly are provided with a plurality of temperature sensors pursuant to UL U419, such that the maximum single value of the temperature sensors on the unheated side of the assembly is less than about 500° F. after about 60 minutes when the assembly is heated in accordance with the time-temperature curve of ASTM standard E119-09a.