Two-sided and two-sided mirrored fire barriers having each of their two sides tested, rated, and certified for use in common spaces, such as spaces shared between two rooms are taught. Two-sided barriers require only one barrier and one installation, instead of the two presently needed. Two-sided barriers may have different construction and composition on each side; whereas each side of a mirrored fire barrier is a mirror image of the other. All two-sided barriers include top-mounted, bottom-mounted, and side-mounted barriers, gas and moisture impermeable barriers, and barriers shaped to fit into the expansion joint spaces created when a plurality of expansion joints intersect. The barriers are disposed to various sizes, lengths, widths, and depths, in addition to variations in shape, content, number and composition of layers, materials, and attachment means required to accommodate the variety of sizes and shapes of expansion-joint spaces and the desired rating, in terms of hours.