My coffee routine is needlessly fussy but fairly predictable. I wander bleary-eyed into the kitchen, add some water to the kettle, and start heating it to 200 degrees Fahrenheit, grind some coffee beans, get out the Chemex, add and rinse a new filter, put the whole thing on a scale, add 40 grams of beans, slowly pour in 600 milliliters of hot water, pour it into my trusty silver Yeti Rambler, and pad into the living room to either play with my son or look at TikTok on my phone. It’s a life, you know?

For the last few weeks, the Ember Tumbler has wormed its way into that routine. The $199 Tumbler is Ember’s newest product but carries the same promise as the company’s popular mugs: it can keep your drink at the exact temperature you want for hours at a time. Its internal heating system will, by default, hold your drinks at 135 degrees Fahrenheit, but if you pair it via Bluetooth to your phone, you can use the Ember app to dial it exactly the way you like it.

The Ember Mug was a fixture in my life for a long time, even though two things about it drove me nuts. It could only hold 10 ounces of liquid — objectively not enough, thankfully there’s a 14-ounce model now — and it was a standard mug with a handle, so I couldn’t take it with me on the train or in the car. (Ember’s first-ever product was actually a travel mug, but it also only held 10 ounces. What are we doing here, people?)

The Tumbler, in theory, solves all my problems! It holds 16 ounces (about 473ml) of liquid, which is a much better number. It also comes with two lids: one with a sliding piece that you can click open and drink out of and one with a handle that closes the mug off entirely. Its battery lasts three hours, which should be plenty of time to finish your coffee or tea. On paper, the Tumbler is everything I’ve wanted it to be.

In reality, it’s a little more complicated than that. For my specific use case, which now involves working from home instead of commuting to an office, it is in fact everything I wanted. The Tumbler is a delightful thing to drink coffee out of every morning. It’s heavy in a good way, like you’re holding a luxury object instead of just a mug; it’s nice to drink out of with the lid both on and off. In the mornings, I bring the Tumbler down to my basement office, set it on the included round charging pad, and my coffee’s hot for hours. Lovely!

As a travel mug, though — like, for people who actually go outside from time to time — the Tumbler is disappointing. I noticed a few times that when I wasn’t keeping it on the charging pad, my coffee seemed to get cold even faster than with my usual travel mug. So I did some testing, comparing the battery-charged Tumbler to my batteryless but well-insulated Yeti Rambler. (There are a lot of good insulated travel mugs out there; this one’s just my go-to.)

First, I poured boiling-ish water into both mugs, and about 60 seconds later (the time it took to find a thermometer), I measured the temperature in both. This was our control number.

• Rambler start temperature: 205.9 degrees Fahrenheit
• Tumbler start temperature: 204.6 degrees Fahrenheit

Then I put the lids on both mugs, closed them, and left them alone for an hour. This is the “I made coffee and then something came up” test. Then I measured their temperatures again.

• Rambler after one hour: 180.7 degrees Fahrenheit
• Tumbler after one hour: 149.4 degrees Fahrenheit

Pros and cons here. The Rambler does a better job of holding its heat, but the Tumbler’s job is to let my drink cool to its ideal drinking temperature — you can set whatever temperature you want in the Ember app for your phone, but it defaults to 135 degrees Fahrenheit, which science (Ember’s app) apparently says is the ideal coffee drinking temperature, and then uses its internal heaters to hold it there. So the rapid decline isn’t necessarily the sign of a problem yet.

Next, I slid open each lid’s mouthpiece and left them out for another hour. This is the “early morning meeting” test.

• Rambler after two hours: 162.7 degrees Fahrenheit
• Tumbler after two hours: 139.2 degrees Fahrenheit

Same deal! The double-insulated Rambler continues to hold its heat, but the Tumbler is at a perfect drinking temperature after two hours. Everybody wins.

For the third hour, I upped the ante. With lids on and mouthpieces open, I stuck both mugs out in the windy 40 degree Fahrenheit elements of my morning. This is the “warm drink on a cold day” test.

• Rambler after three hours: 144.1 degrees Fahrenheit
• Tumbler after three hours: 135.1 degrees Fahrenheit

Once again, I’m calling this a double victory. Both are losing temperature — these are tough conditions! — but are still doing their jobs, and the Tumbler is still in its sweet spot. After three hours, both my beverages are still very drinkable.

I brought both mugs inside, slid their mouthpieces closed, and left them for another hour. This is the “maybe this just became my afternoon coffee instead” test.

• Rambler after four hours: 135.0 degrees Fahrenheit
• Tumbler after four hours: 113.7 degrees Fahrenheit

For the first time, we have a too-cold beverage, and it’s the Tumbler. The battery died right at the end of hour three, as advertised, and now, with no heater and not much insulation, it’s starting to lose temperature quickly. Meanwhile, the Rambler is still hanging on.

My last test was to leave them overnight, which is not exactly a real-world use case, but hey, I’d already poured all the water. I call this the “I left it out overnight” test. 

• Rambler after 12 hours: 99.0 degrees Fahrenheit
• Tumbler after 12 hours: 76.5 degrees Fahrenheit

Obviously, both are undrinkable here, but once again, the Rambler is doing a noticeably better job of keeping my drink warmer. The Tumbler is, for all intents and purposes, at room temperature.

These tests confirmed two things to me. First: the Tumbler does a good job of getting your drink to the right temperature quickly and keeping it there for a few hours. Score one for the fancy mug! But second: if my goal is to keep my coffee hot and drinkable (sometimes too hot!) as long as possible, Yeti’s mug is clearly the better choice. 

The comedian Brian Regan has a great bit where he’s walking around an appliance store shopping for a refrigerator. “This keeps all your food cold for $600,” the salesman says to him. “You’ve got this refrigerator, keeps all your food cold for $800.” Then the salesman walks to the next one, drapes his arm over it, and starts the sales pitch: “Check this out: $1,400, keeps all your food cold.”

That’s how I feel about the Ember Tumbler. It does the job, which in this case, is to keep all my drinks warm. But Yeti’s 16-ounce Rambler costs $30, compared to $200 for the Tumbler, and it actually keeps my coffee above the too-cold level for longer. And if I need it to cool down faster, I can just take off the lid or throw in an ice cube. I’m much more interested in keeping my drink hot than in cooling it down faster.

If you spend most of your time like I do, shuffling from kitchen to basement with the charging pad never more than a room away, the Tumbler works great — when I leave it on the pad, my coffee is at or close to that magic 135 degree Fahrenheit temperature all day. It’s a great mug, albeit a ludicrously expensive one given that my microwave is just upstairs. But when I leave the house, I’m taking the Rambler. Thirty bucks, keeps all my drinks warm.