They are bright orange, keep you warm and afloat, and are probably one reason the three survivors of Monday's helicopter crash stayed alive.
When Southern Lakes Helicopter pilot Andrew Hefford, winch operator Lester Stevens and paramedic John Lambeth were spotted on the shore of Enderby Island on Tuesday they were being kept warm by their immersion suits.
Those suits would also have been bristling with some high-tech equipment.
HeliOtago crew chief Doug Flett yesterday demonstrated the Mustang immersion suits he said were standard kit for crew members.
''You can get quite warm in these things,'' Mr Flett said.
Their buoyancy was such he understood the men who crashed on Monday night did not activate their lifejackets before they swam to shore.
They are, however, bulky.
''They're probably not the easiest thing to swim in.
''To swim a short distance, you've got quite a lot of drag in the water, but you know you're not going to lose a lot of body heat, and at least you're going to stay afloat.''
On top of the immersion suit was a Switlik Aviator Helicopter Life Vest with a buoyancy compensator and pockets for equipment.
Each crew member carried a personal locator beacon, which sent a signal to the Rescue Co-ordination Centre in Wellington.
''If you get separated you've got a much better chance of being found.''
The beacon also had a strobe light on top for extra visibility, and was totally waterproof.
It was attached to the vest so it could not be lost.
Also carried by crew members was a Spare Air device, a tube with a mouthpiece that carried about two minutes worth of air for anyone trapped under water in a submerged aircraft.
''That buys you a bit of time till you get yourself composed and freed from the aircraft.
''Everything in this vest and on his person has got a purpose.''
The radio carried by crew members was waterproof, and could be used to communicate with any shipping in the area.
