Upton, wearing only a white bikini bottom and an opened white parka, was picked as the cover girl for the annual Sports Showed swimsuit issue, exposed on Monday, for the second uninterrupted year.
"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 range and eyesight. My body was shutting down because it was working so hard to keep me warm."


Upton joins personality models including Elle Macpherson, Christie Brinkley and Tyra Banks to appear more than once on the bikini issue's cover.
M.J. Day, a senior editor for Sports Showed, 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 passage after her down there," said Day, who escorted 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