I bought these 12oz double walled glasses because I wanted something to keep tea hotter longer at work. I liked the look of them on the product page, and the 4.5 star reviews gave me confidence in spite of a number of complaining reviews. When I opened the extremely well packaged box, I was very pleased at how attractive they were out of the box, and they certainly made my first cup of tea even more attractive.The first time I used one I noted that it did keep tea hot longer, but not as long as some of the claims in various reviews. Nor did the tea grow instantly cold as some nay-sayers claimed. Out of curiosity,I decided to test both new Kitchables cups against my favorite 12oz medium weight ceramic cup with a handle to see how much difference there really was. I tested both new cups for consistency.I began by ensuring the volume was identical. I used a Pyrex 500ml/16oz measuring cup for this & discovered that all three cups hold 12oz liquid with approx 1/8 clearance at the rim.All three cups were tested at ambient temperature and were at 69 degrees Farenheit. I used an infrared thermometer to measure the outside & inside temperature of the cups before filling (Etekcity Lasergrip 1080 Infrared Thermometer, purchased on Amazon). During the test the cups rested on identical wooden trivets to ensure any heat transfer at the bottom of the cup would be minimal and as similar as possible. To measure the temperature of the water, I used a mercury bulb thermometer I'd had around for a while - faster and more accurate than most instant-read thermometers for this sort of work. During the test I kept the thermometer in hot water that was cooling at roughly the same rate as the cups in order to avoid introducing heat or cold into the first cup I measured. I began by boiling water to a full boil. The temperature was 210 degrees (mercury bulb thermometer) when I poured it (212 is hard to reach and depends on altitude and barometric pressure). I filled each cup to the 12oz mark and measured the outside temperature of the cup with the infrared thermometer. I then checked the water temperature and outside temperature of each cup every 5 minutes for 30 minutes. I discovered that (as expected) the two double-walled cups measured almost identically through the entire test, so I will report them as one cup for convenience.At 5 minutes: glass cup water was 170 degrees, outside was 110 degrees (comfortable to hold); ceramic cup water was 160 degrees, outside was 146 degrees (not comfortable without the handle). 10 minutes: glass cup was 159/107; ceramic 151/138. 15 minutes: glass cup was 145/102; ceramic 140/130. 20 minutes: glass cup was 141/100; ceramic 134/122. 25 minutes: glass cup was 135/96; ceramic 125/116. 30 minutes: glass cup was 126/94; ceramic 120/112.Clearly, the double-walled cups kept the water warmer longer but after the initial 5 minutes they lost heat at approximately the same rate as the ceramic cup. This could be due in part to the fact that the glass cups had a larger diameter at the top than the ceramic cup (3" compared to 2.5"), and so they lost more heat from the larger surface area; also using the trivets may have decreased the heat loss from the wider-bottomed ceramic mug (as might have happened during real-life usage).The initial heat loss was less with the glass cups, likely due to the fact that while the double walls may contain only vacuum as advertised, heat conduction through the continuous glass walls of the container would be less than the solid ceramic walls of the other cup. A matching glass lid would probably help the glass cups retain heat longer, just as keeping the lid on your vacuum-sealed travel cup will. Out of curiousity, since at work I microwave the water inside the tea cup, I tested a glass cup by filling it to 12oz and microwaving it to a visible boil. When measured, the water was at only 205 degrees (any physics expert who can explain that is welcome to weigh in, because I'm curious about that). However, the outside of the cup was at 125 degrees and decidedly uncomfortable to the touch, probably due to the water conducting heat to the glass while it heats. Obviously, though, the beverage would stay hot longer simply because the cup itself wouldn't be cooling it down as soon as the hot liquid is poured into it. And, similarly, preheating the cup with hot water before adding your hot beverage will allow the beverage to be hot longer. So what do I take out of all this? These are attractive cups, although as others have noted they are better for a person with a large hand (me, for example). They keep the beverage warm longer but not profoundly longer, because they are not sealed vacuum bottles or travel cups. Still, if the beverage is still warm 30 or 40 minutes after pouring it instead of feeling cool, that's a win and these glass cups look a lot nicer than the travel mug of your choice. They are very nice to have room temperature water in and guests to my office appreciate a glass rather than a paper cup. Downside: they're tricky to microwave in, because using a hotpad to take them out of the microwave feels insecure on the smooth glass. Because of this, a silicone hotpad might be better than cloth, although I haven't tried one yet.Comments on selected review claims and complaints: 1. They will not keep your coffee hot for an hour, nor will your coffee be cold in 10 minutes. 2. They hold a full 12oz with room to sip. 3. They are not exceptionally fragile. However, when you drop glass on the floor or table, or click glasses with any force at all, it can break. I've had mason jars collapse in my hands just by touching them together - and mason jars are tough.Would I buy them again or recommend them to a friend? Yes. Even though they don't keep my tea hot as long as the ridiculously expensive name-brand travel mug of your choice, they're very nice glasses too look at and to hold..