For folks who have a Libre 2 or 3 CGM sensor and need to wear an adhesive patch to aid in keeping it fixed to the skin. This cover will keep the adhesive from sticking directly to the sensor if the need to change the adhesive patch arises. The larger one is for the Libre 2 and I am unsure how close the fit is for that one, as I currently don't have any of them. The Libre 3 cover does fit perfectly. They are thin enough to enable normal scanning.