Prime Minister John Key is sporting a new holographic wristband that claims to improve performance and keep the body at an optimal "ionic balance" with "free-flowing energy pathways".

The Power Balance wrist band is endorsed by sportsmen such as professional NBA basketball player Lamar Odom and professional beach volleyball player Todd Rogers, but has courted controversy because of a lack of evidence that it does anything.

"When the hologram comes in contact with your body's energy field, it allows your body to interact positively with the natural frequency stored in the hologram," the Power Balance Facebook page says.

"They restore optimal electro-magnetic balance and promote free-flowing energy pathways - NO PROMISES, JUST RESULTS." But last month Power Balance Australia admitted there was no "credible scientific evidence" to support its claim that the wristband improved strength, balance and flexibility. It apologised for its misleading promotions and offered purchasers a full refund.

It is unclear if the Prime Minister believes in the benefits of the band, and he did not return calls last night. A spokesman said it was given to Mr Key as a present.

The wristband was on show yesterday as Mr Key joined volunteers on the runway to model the official Rugby World Cup 2011 official volunteer and staff uniform at the North Shore Rugby Club in Devonport.

Purple, teal and blue jackets, polo shirts and rugby shirts will be worn by 5000 volunteers and 2000 staff members around the country when the Rugby World Cup kicks off in September.

Mr Key, who modelled a polo shirt and matching cap in front of a crowd including Sir John Walker and former All Blacks Michael Jones and Buck Shelford, said volunteers would be an integral part of the World Cup.

"I look forward to wearing this in Cabinet on Monday," said Mr Key.

The garments, featuring mangopare and koru designs, were designed by New Zealand-based company Sportfolio and manufactured by Canterbury clothing.

* Volunteer for the Rugby World Cup at rugbyworldcup.com.