Are Chilly's Tumblers leak proof? Chilly's tumblers are not leak proof. The plastic lid of the Chilly's Tumbler allows for easy drinking and is splash-proof, however it is not leak proof. If the Chilly's Tumbler is knocked over or turned upside down it will leak. Have more questions? Submit a request 1 Comments Date Votes 0 tipcondiane January 13, 2018 12:40 I can confirm the tumbler is definitely not leak proof. It leaks both from where it fits onto the tumbler and also through the drinking open/close slider. Please sign in to leave a comment.