Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: What is the glass made of?
Document: Excellent mug, made out of heavy glass and the etching is nice too. Purchase you will be happy with it.
well, this glass is just great in style, well made, and easy to clean. Although it may get yellow when you drink loose tea, put some baking soda will make it like new again. RECOMMEND to tea lovers.
It's made of great quality, holds 2 cups easily and very easy to clean. I store it with all my Teavana products and use it exclusively for my teas.
i was using theTeavana Contour Tea Tumbler, 16oz, Purplewhich was a waste while sitting at a desk and too tall and overall not to my liking.so i upgraded to this mug coupled with theTeavana PerfecTea Tea Maker, 16ozand it's a match made in tea heaven (and cheaper too).i like the heft of the mug and the process always makes me smile...pure genius!
this is a big solid mug, exactly what i was looking for. strong thick glass.
These are heavy glass cups. Great for keeping the tea hot! Very elegant and beautiful. These are better than average cups found in the stores!
I've had this for a couple of months now and the quality seems good and the glass is pretty thick. Larger than your average coffee mug I use this mostly for tea.
This glass appear sturdy and was well-packed when I received it, but after the first time I used it with hot tea, a split was visible in the glass and it leaked tea.
I wanted to get rid of that funny stuff that clings to some cups........so this is perfect. No problems. And you can pour boiling hot water in the glass without any breakage problems.
Best mug ever! It looks so pretty with any tea inside. I was a little worried about the quality but when I received it, I was completely satisfied. The glass is actually very thick and sturdy!
Answer: glass