The Assam double wall glasses can be used the whole year round. You can use them for your cold drinks in summer and hot drinks in winter. They are made of a very strong but yet light weight glass (borosilicate glass). They can safely go in the dishwasher and microwave. No coaster needed. Bodum's insulated glassware is made from durable borosilicate glass. Borosilicate glass is a strong heat-resistant glass that weighs less than traditional glassware. Used to make scientific lab glass, borosilicate glass (medical grade glass) is stronger than traditional "soda-lime" glass and can be used for everything from drinkware to cookware. It substitutes boron oxide in place of the soda and lime used in traditional glassware. The boron oxide acts as a glue holding the silicate together and due to the small size of boron particles, the glass is held together tighter, resulting in a stronger glass. Some customers may perceive the glass to be "thin" as they hold it. It is important to explain the difference between borosilicate and soda lime glass. Borosilicate glass doesn't need to be as thick as traditional glass to be just as strong. It is simply a different type of glass that is resistant to temperature swings and scratching. Because the particles are held together so tightly, borosilicate glass is dishwasher safe and will not become cloudy over time; you can rest assured that after 100 cycles, the glass will be as clear as the day you bought it. Simply treat it as you would any glass product and it will stand up to every day use. Dishwasher and microwave safe.