What happens in the hot tub ain't stayin' in the hot tub ... These steamy stars may be in for a chill time, but they're definitely heatin' up and keeping social media all fogged up with their HOT hot tub thirst traps!

Heather Graham surfaced above the water in Wyoming to flaunt what 54 years old looks like in a blue bikini 🔥 and Kristin Cavallari sizzled a black two-piece and a cup of joe in her hot tub photo-op!!

"Call Her Daddy' podcast host Alex Cooper knows how to do cold weather ... poppin' some bubbly, while plunging into an outdoor jacuzzi in a pair of fuzzy ear muffs.

YouTuber Nate Garner bulked up for a shirtless snap with the jets in full force and TV personality Joey Zauzig soaked up some winter glow for a flexin' photo!

And, buns n' bubbles for the ladies was a popular theme amongst the celebs ... just take it from British model Demi Rose and influencer Sarah Snyder both showin' off their backsides.

Feelin' chilly this winter? Take a dip into our gallery and heat up with the stars!