Foam, Wraps, and Flammability

Reading a foam spec

Polyurethane foam is the modern stuffing. Choosing it well means reading three numbers that the Polyurethane Foam Association distinguishes ¹:

• Density (pounds per cubic foot, pcf): how much polymer is in the foam. It’s the main indicator of durability - higher-density foam keeps its properties longer. It is not firmness ¹.
• IFD (indentation force deflection): the pounds of force needed to compress a sample by 25% of its height. This is firmness - how the surface feels ¹.
• Support factor: the 65% IFD divided by the 25% IFD, typically 1.5 to 2.6. A higher support factor means the foam firms up as it compresses, so a sitter doesn’t bottom out ¹.

A soft surface with a high support factor gives a seat that feels plush but still supports ¹. A thin seat (a drop-in dining seat) needs firm, high-density foam; a soft thick-looking foam bottoms out on the board.

Practical guidance:

• Seats: the higher-density seating foams a supplier stocks, at a firmness you’ve actually sat on.
• Backs: softer (lower IFD).
• High-resilience (HR) foam: high support factor and durability for premium cushions.
• Buy from a supplier who gives density and IFD numbers, and record them for next time.

Cutting and gluing

• Cut foam with a long serrated knife or, better, an electric carving knife, held vertical; mark lines with a marker and a straightedge.
• Cut cushion foam slightly oversize (about 1/2 inch in width and depth) so it fills the cover crisply.
• Bevel the top edge of seat foam slightly so the cover rolls over without a hard ridge.
• Glue foam to a board or to itself with spray adhesive made for foam, following its ventilation requirements.

Wraps

Wrap foam with polyester batting (Dacron) before covering:

• It softens edges and fills the cover so it looks full.
• It lets the cover slide on during fitting.
• For cushions, wrap and lightly glue the batting, sometimes in a stockinette sleeve, to ease the foam into the cover.

On traditional seats over hair, cotton batting serves the same purpose (see Burlap, Edge Rolls, and Stuffing).

Flammability

Upholstered furniture fires, often started by cigarettes, have killed many people. The U.S. rule today is 16 CFR 1640, which made California’s TB 117-2013 smolder-resistance test a federal standard ²:

• It covers cover fabrics, barrier materials, resilient fillings, and decking materials ².
• It took effect June 25, 2021; the permanent label, “Complies with U.S. CPSC requirements for upholstered furniture flammability,” became required June 25, 2022 ³.
• It applies to furniture reupholstered for sale. Reupholstery for personal use is exempt ³.

TB 117-2013 is a smolder test, met with smolder-resistant fabrics or barrier layers rather than added flame-retardant chemicals. If you ever sell reupholstered work, use compliant materials and label it; for your own pieces, choosing smolder-resistant fabrics and barriers is still sensible.

What to take from this

Foam density predicts durability, IFD measures firmness, and support factor (65%/25% IFD) predicts bottoming out. Use firm, high-density foam on seats, cut oversize with an electric knife, bevel edges, and wrap in polyester batting. Upholstered furniture sold in the U.S. must meet 16 CFR 1640 (TB 117-2013 smolder resistance) with a permanent label; reupholstery for personal use is exempt.