Does your homemade mask work?

If a surgeon arrived at the operating theatre wearing a mask they had made that morning from a tea towel, they would probably be sacked. This is because the equipment used for important tasks, such as surgery, must be tested and certified to ensure compliance with specific standards.

But anyone can design and make a face covering to meet new public health requirements for using public transport or going to the shops.

Indeed, arguments about the quality and standard of face coverings underlie recent controversies and explain why many people think they are not effective for protecting against COVID-19. Even the language distinguishes between face masks (which are normally considered as being built to a certain standard) and face coverings that can be almost anything else.