The moisture sandwich is a trending skincare phrase that refers to the process of layering your skincare products to reduce transepidermal water loss. The rule of thumb for moisture sandwiching is to apply moisturizer to skin that’s dampened with a facial mist or water. This technique allows for better product penetration and can enhance your skincare experience. One disclaimer. Don’t try it with retinol or exfoliating acids, as doing so can be irritating to your skin.