Passive fire barrier is heavy-bodied, single-part latex designed for use on construction materials such as oriented strand board, structural insulated panels and framing lumber. It also is used on aluminum and steel sheets, round and box steel columns. When activated by heat or flame, a dense carbon char is formed separating and shielding the substrate from heat while off gassing displaces oxygen from the treated surface; thus eliminating two of the three components needed for combustion.