The magazine tested one upgrade filter and seven of the most commonly used cycle masks for leakage, for how much foreign matter gets into them and for how much carbon dioxide breathed out by cyclists doesn't get out. Many did not come out well, despite their manufacturers' claims.

Ozone

The main reason cyclists use masks is to filter out harmful pollutants linked to many heart and lung diseases, including asthma, and ozone, which causes sore throats, breathing difficulties and watery eyes.

The tests found that the price of the mask is no indicator of how well it works. The cheapest mask in the test - Kanco Eezy Breethe - scored well for leakage and filtering out pollutants.

European standards

It was one of three products which did well in keeping out normal and ultra-fine particles of pollution. The others were Respro Techno Gold and the Techno Gold Upgrade Kit.

Cycle masks have become very popular

Masks which passed the European Standard test for particles, known as BS EN149, generally did best in the tests.

Masks that scored poorly included Airwair Neo Face Mask, Airwear Outlaw Biker Scarf, Freeway Basics Cyclist's Face Mask and Respro Urban Survival City 149.

'Health Which?' says many of the manufacturers claim their masks can filter out harmful gases.

Dubious

But it is dubious about the way they test these claims.

It believes the conditions in which the masks are tested may be "unrepresentative" of the conditions many cyclists will encounter on the road.