ZEISS Fog defender system is an easy-to-use solution that keeps your lenses from fogging for up to 3 days, even while wearing a mask. One spray of the fast-drying solution will provide fog-free vision for up to 72 hours. Simply spray and wipe dry with the supplied microfiber cloth. The date printed on the package is the Production Date. The product is good for at least 3 years from the production date.