Fels-Naptha soap is usually available at Walmart, though stock varies by location. Walmart also sells the soap on its website, as of August 2015. Fels-Naptha is a laundry bar soap manufactured by Purex and is used to remove stains.
Fels-Naptha soap is a common ingredient in homemade powdered laundry detergent recipes. Other ingredients include borax and washing soda. Some recipes also call for baking soda and oxygen bleach. Most Walmart locations also carry the other needed ingredients.
People can use Fels-Naptha soap as a stand-alone stain remover by wetting the bar, rubbing it over stains and laundering clothes as normal, according to the Purex website.