Whether you call it a sleeve, jacket, or Koozie, it's perfect for protecting your glass jar from breakage and your hand from cold or heat. Personally, I usually reach for a wide mouth pint jar for drinking, but regular mouth pint jars are more common. The silicone sleeve adds grip, looks great, and I love the feel of it in my hand. 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. The regular mouth pint sleeve is a little squared, just like the jars. They won't fit a wide mouth pint jar. 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.