Review on S'well 18 oz Azurite Vacuum-Insulated Tumbler with Clear Slide-Open Lid - Keep Drinks Cold for 12hrs, Hot for 4hrs - BPA-Free Stainless Steel Water Bottle by Yadira Hernandez

Comparing the performance of this mug to my 16oz Yeti Rambler warming mug, I was quite surprised. Using a milk thermometer, I monitored the temperature in both mugs for a couple of hours and then throughout the night. Results? Almost equal. Why was I surprised? Because S'well is noticeably thinner, which almost always means poorer heating/cooling performance. Surprisingly not here as this mug matched my Yeti. So the perfect cup? Well...not much if you're looking for an airtight lid. It helps if it tips over, but it's definitely not airtight, which is what I look for in a coffee mug when I take it to work. Don't worry at home. All in all a stylish mug with excellent heating/cooling performance. Just don't buy expecting a sealed lid.