Bear Grylls has had a whole host of celebrities test out their survival skills on his adventure TV series. 

But when asked who was the toughest, the British survivalist gave a surprising response. 

The 50-year-old appeared on Australia's The Project on Friday night and said he often finds women impress him more than men when it comes to coping in tough conditions.  

'Often, I think the girls outshine the men actually' Bear admitted. 

'I quite like seeing that dynamic of, you know, survival is a great leveller, it doesn't care who you are, what you like, and invariably people are actually pretty impressive.'

When it came to naming a standout participant, Bear said Natalie Portman, who appeared on Running Wild With Bear Grylls in 2022, wowed him.  

'I think of Natalie Portman recently. She was incredible. You know, she is tiny, but just unstoppable' he said. 

Bear said that tennis champion Roger Federer also stood out. 

'He's just such an incredible guy, a positivity and determination and courage in big moments, and I think there is a commonality, isn't there, between difficult moments in life, difficult moments in a jungle, difficult moments in sport' he said. 

'It requires you to dig deep sometimes, and that's a good thing.' 

Actress Natalie, 43, kicked off the 2022 series of Running Wild With Bear Grylls: The Challenge on National Geographic in the wild landscape of Southern Utah, where she learned how to descend various canyons.

There was one challenge Natalie wasn't completely on board with, declaring Bear's unique method of filtering water as 'gross.' 

After trekking through the canyons, Natalie and Bear finally discovered a shallow pool of water. 

Bear explained to the actress that they would need to filter and boil the sludgy water before they could drink it.  

'This water is really full of loads of dead flies and dirt and everything,' he explained before musing with Natalie what they should use as a filter.

'We could use a sock, but then again, you kinda need your sock,' he said, before offering up his underpants.

'We're gonna filter sludge water through underpants?' a shocked Natalie asked. 

Bear got to work cutting away at his underwear with his knife after Natalie asked if he 'wanted some privacy.' 

'I mean it's not going to be perfectly clean,' he told the star, and she quipped back, 'That's an understatement.'

Grylls is currently in Australia on his Never Give Up Tour.