WHAT DOES SLS FREE MEAN?...that our natural MP soap base doesn't contain Sodium Laurel Sulfate...it is also SLES free...meanin' that it doesn't contain Sodium Laureth Sulfate either...both are a detergent & surfactant found in many personal care products i.e., soaps, shampoos, toothpaste etc....it's an inexpensive & very effective foamin' agent...they're chemical relatives...i hope this helps...thanks for your ?...crystal