The group, led by high-school teacher Blake Leonard, 27 from Wollongong, are trying to raise $100,000 for charity beyondblue.

"We were looking to do something outside of the norm, something risky and fun that will push us to the limits," he said. "The myth of the superhero teacher in the American movies doesn't really exist. This is a way to be there for students outside of assigned hours."

Other group members, who all live south of Sydney, are Ben Anderson, 35, Adam Leonard, 28, James Raxworthy, 27, and Michael Hole, 35.

They have already raised $21,500 towards their target amount.

"We knew that for us to look legitimate and not like five clowns, we would need the backing of a trustworthy charity," said Mr Leonard.

"We thought that they would do a good thing with the money. We've followed them for a long time and donated to them in the past."

The group will be walking the total 20 kms together wearing only shoes and budgie smugglers, from Seaman's Hut, at the top of the Mount Kosciuszko chairlift, to the summit and then back.

They have allowed themselves a four-day window, between July 4 and July 7, so that the trek can be done under the best available weather conditions.

Average temperatures are expected to get to only -1 and -2 degrees Celsius for the week.

"The body is incredible, the body can keep pushing, but your brain quits a lot sooner," said Mr Leonard.

Chris Tzarimas​, director of the Lifestyle Clinic at University of NSW Faculty of Medicine, is concerned about the health risks and implications of the challenge.

"I hope they raise a lot of money, because I think it's more of a high risk to their personal safety and wellbeing than it is an endurance challenge," he said.

Mr Tzarimas said that the risk of getting hypothermia - a dangerously low body temperature - is high, and if one of the team fall victim to it and can't get treatment, they could be dead within half an hour.

"Blood gets redistributed from the skeletal muscle to the vital organs to maintain warmth," he said.

"The problem is that they're doing something physically active and so their skeletal muscles are going to require significant blood flow. You hope that will generate enough heat to keep their vital organs warm, because that's what you need to keep them alive."

Mr Tzarimas said that in these extreme conditions, it wouldn't take much for one of the group to get hypothermia.

"It doesn't even necessarily have to be sub-zero temperatures," he said. "It's more or less about your core temperature."

Normal core body temperature is 37 degrees Celsius, and hypothermia can set in when core temperature falls below 35 degrees Celsius.

If this happens to one of the group and they don't receive immediate medical treatment, Mr Tzarimas said they would only have between 20 and 30 minutes to live.

Mr Leonard said that the team completed a trial run of the trek in board-shorts, and they were acclimatising to the extreme conditions using ice baths.

The team is aware of the risks involved, and they plan to have an emergency team on standby during the challenge.

Mr Tzarimas projects they will need it. "The more physically conditioned they are, the lower the risk is because they are more acclimatised to the conditions," he said.

"This is life and death stuff."