Whether you call it a Koozie, a Kozie, a Coozy, a Cozy, or just an insulating sleeve, it's perfect for protecting your glass jar from breakage and your hand from cold or heat. FDA food grade silicone rubber is dishwasher, freezer, and microwave safe! Silicone is a safe, extremely durable, non-plastic (BPA free) material for food use that does not leach any chemicals. I always have a quart of water sitting on the corner of our kitchen counter or my computer desk. The silicone sleeve adds grip, looks great, and I love the feel of it in my hand. A big jar means I don't have to fill it as often, so I drink more water. We designed the sleeve to fit tight enough that it won't fall off, but loose enough that it is still easy to get on and off. Different brands and mouth sizes of jars will vary a little in size, but it should stretch to fit almost any of them. Use a different color for each family member, and stop wondering which beverage cup is yours! Microwave safe means you can heat up your beverage without removing the sleeve. Or take out a frozen jar of food, put a koozie on it, and heat it up. Since they don't touch your beverage, I often just rinse them, but they are also dishwasher safe. You can leave them on the jar, but I find that water gets trapped so I prefer to separate them to clean the jar.