High Quality Hand Blown Borosilicate Glass Tumbler Borosilicate glass is well known for its durability and resistance to thermal shock This means it will not crack under extreme temperature changes like regular glass.It has the ability to go straight from a freezer to an oven rack without cracking.For you, this means you can pour boiling hot water into borosilicate glass Mug without worrying about shattering or cracking the glass.While Borosilicate is far more durable and resistant to thermal shock than other types of glass, it is glass so breakage is still a possibility.However, when broken, borosilicate glass tends to crack into larger pieces rather than shattering (it will snap rather than splinter), making clean up less hazardous than a typical glass.Borosilicate glass is hypoallergenic, lead-free and unlike a plastic straw, it is BPA-free.Have peace of mind knowing that no toxins are being leached into your beverages as you consume them! .Double Wall Construction for Hot and Cold Drinks Double layered glass mug insulates your drink keeping it hot or cold longer while the outside stays comfortable to your touch allowing you to embrace your drink while you sip at your drink's ideal temperature.High-quality FDA Food Grade Tested Silicone Silicone Seal to prevent any leaking while drinking Silicone sleeve to ensure a non-slip grip Silicone base on the bottom for glass protection Size 410mlWorry FREE Purchase as we stand behind our products with our Unconditional Satisfaction Guarantee Click "Add to Cart" now to drink your perfect cup of coffee