The Number 1 anti fog measure in the US for 15 years, now available in the UK. 

Amazon describe it as: This is one of our most popular selling product lines and is great for cleaning and polishing glass and plastic. It also repels lint and dust and prevents fogging of lenses. Great for eyeglasses, ski goggles, swim goggles, face shields, sunglasses and binocular lenses.

Webbikeworld said: this stuff works..It's a green-colored wax-like substance that seems to transform into a near-liquid state as soon as it absorbs heat from a finger.  It's applied by rubbing a very little amount on the inside of the visor.  Then buff it out using a clean, soft, dry cloth.  It definitely disappears, leaving no trace whatsoever. The small container holds 0.25 oz., and measures only 40mm across by 18mm thick, so it's easy to fit just about anywhere.  It only takes a very, very thin layer to be effective, so a 0.25 oz. tub should last a long time. 

Cat Crap anti-fog comes in a handy pot, ideal for the pocket inside your leathers - all you do with it, is rub some on the inside of your visor, then buff it off with a clean cloth - no streaks, no spray bottles, no fog!

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