Ben Freeman does the opposite: he strips down to his swimming togs and jumps into a pool.

Freeman, 21, whose sport of choice is ice swimming, seeks out water below 10 degrees.

He's the guy who buys bags of ice at petrol stations to fill up his bath tub for training.

Freeman became the youngest Australian to complete an "ice mile" when he swam at Lake Crackenback, water temperature 4.6 degrees, earlier this month.

Freeman was just the fifth Australian to complete the swim.

The ice mile requires a water temperature below five degrees to be ratified by the international ice swimming association.

He trained eight to 10 hours a week, aiming for speed, mostly at Phillip pool.

And each afternoon he jumped in his neighbour's pool, temperature 8 degrees.

"I'd swim in there for half an hour to 45 minutes to get really cold, then I'd hop out and wrap up and just let my body recover naturally," Freeman said.

"I mixed that up with getting three to four bags of ice from the service station and sitting in an ice bath for 20 minutes to prepare my body, even wearing shorts and a T-shirt outside all day was a way of acclimatising my body."

Freeman decided to try the sport when he was training to swim across the English Channel.

He trained first at Thredbo, but encountered water that was frozen over - a challenge even for this extreme swimmer.

"When we went to do the mile it was frozen. We got a kayak out on the water to try break up the ice and gave it a couple of hours in the sun to hopefully melt a little bit but it was just too frozen.

"So we ended up having to go to Lake Crackenback," he recalled.

The extreme training has been tough but helps his body tolerate the shock, and even could be the thing that saves his life.

"I was a little concerned about the shock, a lot of people with no experience will start hyperventilating and panicking, a lot of people will die just from the panic," Freeman said.

"I ended up being fine with it, but I was confident in my preparation and my body tolerated it fine.

"I had so much adrenaline going through my body that it wasn't actually too bad.

"I swam the first hundred quite quick, then after three or four minutes my hands started going numb and I couldn't feel them and then in the last few hundred metres my arms were so heavy.

"Once you start to get dizzy or confused that's the time to pull out, you've spent too long in there."

He had nine supporters, including one monitoring progress from a kayak.

"If my strokes got too slow or my body position started to drop or sink or if there was any sort of dramatic signs they would pull me out," Freeman says.

Freeman has the ice mile under his belt, but he has still more to tick off on his ice swimming wish list.

Now, he's eyeing the world championships in Poland in 2021.

And for yet another challenge, "I'd really like to compete in an iron man too", he laughs.