The Swiss Guards, the world's oldest standing army, are getting some new headgear.

The Pope's army plans to replace their metal helmets with plastic PVC ones made with a 3-D printer, giving them cooler and more comfortable headgear when standing guard for hours at a time.

The Swiss Guards unveiled the helmet prototype before their annual swearing-in ceremony.

Thirty-two new recruits - all of them single Swiss men under age 30 and upstanding Catholics - will join the small corps for a minimum of two years by pledging to protect the pope and his successors.

The new helmets will not be donned on Sunday since more formal helmets are used for the elaborate, pomp-filled swearing-in ceremony in the San Damaso courtyard of the Apostolic Palace.

But Swiss Guard spokesman Sgt Urs Breitenmoser said the Guards hope to replace their existing metal helmets by next year if they can find sponsors to pay for the new ones, which cost around €880 apiece, half the cost of the old ones.

The Swiss Guards are famous for their billowy blue, red and yellow striped uniforms. According to a history on the Guards' website, the "Gala Uniform" as it is known, was designed by Commander Jules Repond in the early 1900s and is based on the colours of the Medici family.

It is only one of several outfits the guards wear. Those policing the Vatican's main entrances don far more sober navy uniforms topped with a beret for their regular shifts.

The corps, which historians consider the oldest standing army in the world, was founded in 1506 by Pope Giulio II.

Tradition has it that he was so impressed by the bravery of Swiss mercenaries that he asked them to defend the Vatican.

Ever since, for more than 500 years, Switzerland has been supplying soldiers to the Vatican.

The May 6 date for the annual swearing-in ceremony commemorates the day in 1527 when 147 guardsmen died while protecting Pope Clement VII during the Sack of Rome.