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How to keep your glasses from fogging up
Purchase an anti-fog product to treat your glasses at home.
Many companies manufacture products specifically designed to prevent glasses from fogging. These are either a spray or gel, and when applied directly to your lens, will prevent fog by forming a barrier that protects against temperature change and moisture.
Most products require you to spray both sides of the lens, let dry, and wipe clean with a soft, dry cloth. Some products suggest longer dry times, while others require the spray or gel be rinsed off prior to wiping.