Thermos Bottle Day is celebrated annually on February 26, recognizing the Thermos brand, which has become synonymous with vacuum flasks designed to keep liquids hot or cold. The Thermos bottle features two compartments with a vacuum in between, preventing heat or cold from escaping. The brand produces various items, including food jars, mugs, tumblers, coolers, and lunch boxes. While the specific customs for celebrating this day are not detailed, it is likely that enthusiasts of the Thermos brand acknowledge the day by using their products or sharing their benefits. The day serves as a reminder of the Thermos' historical significance and its evolution from a patented invention to a widely recognized household name.