For the past four years, we’ve been conducting temperature tests to determine which model keeps water cool for the longest time. Here are the results obtained in 2017:
Internal temperature increase over 24 hours
Internal temperature increase over 24 hours KYLE FITZGERALD / WIRECUTTER
For this test, each bottle was filled with water at 8 ° C. We then measured the water temperature every hour for ten hours. Over the years, we have found that all insulating cylinders achieve roughly the same result. Brands like to highlight their models’ cool or warm talk time, but basically you can buy any insulated running water bottle since they all get the same result.
This year, we’ve tried to illustrate the expected difference in interior temperature between an insulated bottle and a non-insulated bottle. We filled each container with the same amount of water, about 12 ° C, and measured the temperature exactly 17 hours later.
Internal temperature increase over 17 hours. The lower bars indicate better maintenance of freshness.
Internal temperature increase over 17 hours. The lower bars indicate better maintenance of freshness. KYLE FITZGERALD / WIRECUTTER
In this case, a slightly fresh liquid without ice cubes, after seventeen hours in the insulated flasks, remains at a temperature five to six degrees lower than room temperature, while the water in the non-insulated flasks is at room temperature. That’s pretty much the difference between standing in the shade and standing in direct sunlight.
You can buy any insulated bottle: they all get the same results.
Manufacturers of gourds and bottles now boast a new feature: a copper lining to keep them hot or cold. This method may well work and, as Wesley Johnson, cryogenic research engineer at NASA’s Glenn Research Center in Cleveland, points out, “a similar technique is often used for the isolation of spacecraft. Beyond being generally an excellent conductor, copper is used for insulation because heat is transmitted in three forms: solid conduction, gas convection and radiation, as we have been reminded. Wesley Johnson. A double-walled gourd already intercepts solid conduction and a vacuum-insulated walled bottle prevents gas convection. “This leaves only the transfer of heat between the walls by radiation, which represents a factor about ten times less than solid conduction or convection,” says Wesley Johnson. And copper can be used to block the latter way of losing or gaining heat.
But it only works in very specific circumstances. According to Wesley Johnson, “the primary advantage of copper, when polished, is that it reflects radiation transfer much better… the copper lining must therefore be shiny, installed under vacuum and in a way that limits oxidation of the metal before sealing the vacuum. “
We have tested gourds with and without a copper liner and have not seen any benefits from using it. The Yeti Rambler is “made with a copper plate that protects from UV rays,” according to its communications officer. Ditto for the Otterbox cups, which we studied for another buying guide. But neither Klean Kanteen nor Hydro Flask include copper in their composition materials.
We have carefully studied the proportions of these bottles. For large bottles, the creators sometimes tend to lengthen them, making them taller and thinner. These tip over easily. Other designers bet on the width, transforming the flask into a real weapon: the S’well 74 cl could indeed pass for a small baseball bat.
We also looked at where we put our lips: if we drink directly from the bottle, what does it feel like? We also judged the bottles based on the cap options they offer and their versatility. Does the bottle fit in a cup holder? Can it contain hot drinks? Someone will always find someone to put hot liquid in a water bottle, even though an insulated travel mug would be a better idea and prevent the bottle from forever tasting like cold coffee.