As new variants of Covid-19 spread around the world, we're all a little worried about the strength of our masks. New guidelines are now emerging from various health agencies around the world recommending that everyone should double-mask: that's a cloth mask over a medical mask. So how do we best do that? Is it a sure-fire way to keep us safe from the aerosol transmission of Covid-19? What's the difference between a mask and a respirator? And how can we know if the masks we’re buying are the real deal or counterfeit products?