I'd been using an old Klean Kanteen Wide Insulated bottle for my daily coffee for years and years and years. Since 2009 I guess. It'd been through hell and back. Probably 15,000 miles of bike commuting, rattling in my bottle cage. More drops can I care to admit. It'd also been on camping trips and Sunday shopping excursions, and everything else under the sun. It had been my constant caffeinated companion for 8 years straight, until a month ago. The o-ring in the cap needed to be changed again, as it did about every 9 months or so. The o-rings wear out. But Klean Kanteen's website was fresh out of spare o-rings. So I decided to rethink my choice of coffee thermos, and maybe try something new, that wasn't so beat up and dented. I'd had lots of good luck over the years with Hydroflasks for water bottles, and bought a new Hydroflask locally. It seemed perfect for about 2 whole weeks. Then this odd burnt looking spot began forming in the bottom of the bottle. The spot was ugly, but I just figured that it was a coffee stain. It happens. Then about a week after the spot formed, I noticed that my coffee wasn't so hot after my bike ride to work. The temperature of my daily coffee quickly turned to absurd. I thought it was my coffee maker at first, but a test with a thermometer quickly disproved that theory, yielding a steady temperature of 200 degrees. Yep. You guessed it. The Hydroflask went bad. My guess is that spot is contamination leaking through into the inner wall of the Hydroflask, meaning my coffee was flowing in between the inner and outer walls. So much for Hydroflask. I'm going back to my flat out amazing and dependable insulated Klean Kanteen. Even after all these years, my coffee is still piping after lunch time. If you look at the above pick with a close eye, you'll notice that this experiment was not all for naught. I found that the much nicer Hydroflask coffee cap works perfect with my Klean Kanteen. I even filled the bottle with coffee and left it on a paper towel overnight, to make sure there were no leaks. After 12 hours upside down, here's the clean paper towel to prove the test. Not even a hint of a leak.