Cotton material is a pleasant natural fabric that absorbs and breathes well and is strong and durable. Whitening yellowed cotton material can be done with household bleach, but bleach is ultimately harmful to cotton fibers, breaking them down and leading to frays and holes. A better method is to soak the yellowing material in one of several solutions, and then allow the sun to naturally bleach out any remaining yellowness. The sun alone is enough to whiten some cotton fabric.
Add one cup of one of the suggested cleaners to the washing machine and allow it to fill with hot water.
Add the yellowing cotton material to the washing machine. Allow it to cycle through to the wash and agitate stage, but stop the machine before the rinse cycle. This should be between 10 to 20 minutes once you start the machine.
Allow the yellowing cotton material to soak for two to six hours in the washing machine.
Resume the washing machine's cycles. Once it stops, check the material to see if it has whitened. If not, repeat the steps.
Blot the material between two layers of towels. Do not wring the fabric. Wringing causes fibers to break and eventually fray. Blot the cotton material by laying it between the towels and pushing with the palms of your hands on the top towel so that the towel absorbs as much of the moisture in the fabric as possible.
Allow the material to air dry in the sun.