The claims of 8-hour plus heat retention are absolutely true, and sometimes I'll make my scorching hot black coffee the night before so it's the perfect temperature when I get to work the next morning. I haven't tested its leak-proof abilities but in everyday kind of use, I've not had any issues. Keep in mind this item requires user care in keeping all the parts (lid, gaskets/rubber seals, sippy thing) clean. It also keeps my cold brew chilled all day. Chuck a few small ice cubes in the flask and you're good to go. Highly recommend.