John Marsey and his cousin Darren Lines were frying bread in Jenny Marsey's kitchen in Hartlepool, northeast England, on Sunday when their meal caught fire.
Lines grabbed the nearest thing from a pile of laundry to put it out: his aunt's billowing, powder blue, size XL underpants.
He ran them under the faucet and tossed them onto the flames, successfully smothering the fire, a spokesman for the Cleveland Fire Brigade said, speaking on condition of anonymity in line with department policy.
Lines' swift thinking saved the kitchen - but left his aunt's underwear slightly scorched.
"It could have been a lot worse," she said. "My family could have been in hospital but the knickers saved the day. I'm just grateful to the boys."
The fire official said the general principle of using a large, wet cloth to cover a grease fire was a sound one.
As for using underwear: "Clearly it depends on what size you are - but I don't want to go there."
