The most important feature of onion goggles is their ability to stop the vapour from cut onions entering your eyes and irritating them.
• Why do onions make me cry?
When onions are cut, an enzyme called sulfoxide lyase and sulfuric compounds are released from the broken cells. When exposed to air, they react with one another to form a vapour that irritates our eyes and causes us to cry.
•How do onion goggles work?
Onion Goggles work by having a layer of soft foam rubber on the inside of the frames. This layer is meant to seal the gap between your face and the frames of the goggles and so stop the vapours from entering your eyes.
So clearly the fit is of primary importance because any small gap allows the vapour in to your eyes. Unfortunately anyone who has ever worn onion spectacles (sometimes wrongly called goggles) will tell you there are always small gaps.
•How do I get goggles that will fit my face shape?
Professional goggles get around this problem by having an adjustable cord to pull the frames gently against your face and so closing the gap. Think about swimming goggles and how they work.
Depending on your face shape putting a piece of string on the ordinary shaped onion spectacles can sometimes help but usually doesn't work very well as the string tends to slip along the ear pieces and lifts them upwards and away from the eyes.
•Any bad things about onion goggles?
Very occasionally a side effect of closing the gap means that sometimes because there is no ventilation inside the goggles the lens will mist up slightly. But this only happens very occasionally and only in unusual circumstances. Anti-mist coatings only work if there is ventilation or in other words when the vapours can get in.
(Never use rain x or any other product sold for car windscreens, they are designed for glass and will permanently spoil your plastic lenses leaving them looking milky.)
The best tried and tested solution if this happens is to wipe a tiny drop of washing up liquid or soap all over the inside of the lens and dry it off with a soft dry cloth. This leaves a very thin layer that breaks up the surface tension and prevents the condensation from forming. Try it on your bathroom mirror.
•Can I use them for anything else?
Many people who have onion goggles also use them when barbecuing or attending bonfires to effectively keep the smoke out of their eyes.
It's a good idea to replace the goggles in their protective case when you've finished with them that way they stay clean ready for next time. It also helps to prevent other people trying them on and 'borrowing them'.