Bell have joined the aero helmet fray by launching the Star Pro, which has sliding vents to optimise aerodynamic performance and ventilation.

Aero road helmets have become increasingly popular in the professional peloton, with Giro unveiling the Synthe ahead of the Grand Départ, and we spotted Sep Vanmarcke of the Bell-sponsored Belkin Pro Cycling team wearing the Star Pro ahead of stage two in York.

Bell launched a new aero helmet ahead of the Grand Depart. The Bell Star Pro, modelled here by Belkin Pro Cycling's Sep Vanmarcke, has vents which can be opened or closed to improve either cooling or aerodynamics.

Bell say the Star Pro is the first "dual purpose" helmet thanks to its 'Active-Aero Technology', which is essentially a switch at the rear of the helmet which opens and closes the lid's vents. That allows the rider to optimise either ventilation or aerodynamic performance, though it doesn't necessarily allow for both at the same time.

"Our intention with Star Pro was to eliminate the either/or choice cyclists have long been faced with when it comes to being faster or cooler," said Bell's Azul Couzens.

Naturally, the helmet has been wind tunnel-tested, using wind-averaged drag (WAD), a wind velocity of 25mph (40kph) and a 30-degree head angle to pit the Star Pro against a number of rival aero lids. And the results? Bell say the Star Pro, with vents closed, is the fastest helmet on the market "when compared to other very well-known aero competitors" (though they don't specify which), and when measuring cooling efficiency with the vents open, it proved to be "near equal" to a traditional road helmet over a 30-minute period.

The Star Pro will be available from January 2015 with or without a magnetic visor for £199.99 and £169.99 respectively

Bell Star Pro aero helmet with magnetic visor (Pic: Bell)

That cooling is helped, according to Bell, by the helmet's 'Overbrow Ventilation', which is said to draw cool air into the vents and circulate it through the helmet via a number of air channels that then push warm air out through the exhaust ports. Otherwise, the Star Pro has a two-layer EPS construction, which uses a softer density foam on internal sections and a stiffer foam on external areas. The new 'Float Fit System' allows for vertical adjustment.

The Star Pro will be available with or without a 'Magnetic Zeiss Shield', for £199.99 (with shield) and £169.99 (without shield) respectively. It will also come in six colours and three sizes. Except to see the Star Pro in Bell retailers from January 2015.

Website: Bell Helmets

UK distributor: Zyro