The Pillow Lock System comprises of four self-adhesive hook-and-loop patches which are supplied with all Sea to Summit sleeping mats (as of Spring 2019). Attached to your sleeping mat, these patches secure your pillow and prevent it slippingyet they will not snag on clothing or other lightweight fabrics. All Sea to Summit Pillows (as of Spring 2019) are compatible with this system. Existing pillows can be made Pillow Lock compatible by adding an Aeros Pillow Case. The Pillow Lock System is only approved for Sea to Summit sleeping mats and we do not recommend placing the stickers on other brands of sleeping mats.