Gerard Butler puts ice down his underpants to cool off.

The Hollywood hunk claims it was so unbearably hot when shooting terrorist attack flick 'Olympus Has Fallen' in Louisiana - a state which boasts excessively hot and humid summers - he packed his underwear with ice blocks to lower his body temperature, a trick he learned when making 2003 movie 'Timeline'

He laughed: ''Here's a trick I use: put ice on the balls. I learned that on 'Timeline', which was shot in Montreal when it was nearly as hot. We put packs of ice down our underwear.

''I don't think its good for the reproductive system, but it cools down your whole body. And focuses the mind, shall we say.''

Despite the 43-year-old actor risking lasting damage for the sake of his craft, he admits the trick didn't quite work since the gruelling shoot still left him gasping for breath and bathed in sweat.

Gerard admitted in an interview with ShortList magazine: ''Over the week we probably did 400 takes; the sweat was dripping off me two drips a second.''