Is there a natural way to soften cloth diapers? Washing your diapers in cold water will soften them. The colder the water, the softer they’ll become. Lemon juice can soften your diapers. Add 4 teaspoons (20 grams) of lemon juice to warm water, and soak the diapers for an hour before washing. Vinegar softens as well as sanitizes fabric. We recommend using not more than 1/4 cup of white vinegar in the rinse cycle.