"It was freezing," Upton, 20, told NBC's morning TV show "Today" on Tuesday. "I'm from Florida, so it wasn't easy for me.
"When I came back, I was losing my hearing and eyesight. My body was shutting down because it was working so hard to keep me warm."
Upton joins celebrity models including Elle Macpherson, Christie Brinkley and Tyra Banks to appear more than once on the swimsuit issue's cover.
M.J. Day, a senior editor for Sports Illustrated, told Reuters that Upton braved temperatures as low as 24 degrees Fahrenheit (-4 Celsius) and wind chills as low as -20 Fahrenheit (-29 Celsius).
"We should name a passageway after her down there," said Day, who accompanied Upton on the frigid shoot. "She braved six days in a bikini while we were head-to-toe in jackets ... No one will ever accuse her of being a whiny model, ever."
This year's 17 models were part of photo shoots that stretched across all seven continents.
