How kitchen sponges are made

The holes in a cellulose sponge start as salt crystals that melt away inside a hot mold.

stations: 7
things upstream: 46
raw sources: 13
steps from the ground: 8

The short version

Cellulose sponges start from viscose: wood cellulose dissolved with caustic soda and carbon disulfide. Fibers such as hemp or jute and crystals of sodium sulfate are kneaded in, and the paste fills big molds. Heating solidifies the cellulose while the salt melts and drains out, leaving pores. Blocks are washed, bleached, dried and cut. Synthetic sponges use polyurethane foam instead.

Turn cellulose into viscose

Cellulose is treated with caustic soda and carbon disulfide in a closed reactor. The product dissolves to a thick liquid called viscose, which ripens and is filtered.

Goes in
Wood pulp Caustic soda
Knead in fiber and crystals

Strength-giving fibers such as hemp or jute go in with sodium sulfate crystals. Crystal size decides pore size, with bigger crystals making a coarser sponge.

Goes in
Flax
Heat in big molds

The paste fills large rectangular molds and is heated. The crystals melt and drain through openings in the bottom, while the viscose regenerates into firm, porous cellulose.
Wash and bleach

The blocks soak in a vat of bleach, then rinse in water to remove soluble salts and make the material flexible.

Goes in
Bleach Water
Dry and slice

After drying, an automatic cutting machine slices the big blocks to size. Many plants sell blocks on to converters for this step.
Bond on the scourer

A scouring pad can be laminated to one face with sponge glue, and antibacterial agents can be added.

Goes in
Polyester Adhesive
Wrap and box

Finished sponges are wrapped and boxed for sale.

End of the lineKitchen sponge

Worth repeating

Competitors in the ancient Olympic Games bathed with sea sponges soaked in olive oil or perfume.
Some sponges can harbor Salmonella for more than seven days.