Laboratory grade borosilicate glass can be rapidly heated or cooled without cracking. This guy is great for collecting hydrometer or refractometer samples, weighing hop additions, or mixing water treatments.
I was skeptical at first due to the small size but I actually use this thing quite a bit. Everything from rehydrating dry yeast, cooling wort for SG readings, sampling wort, starch conversion, or even just to freak my neighbors out by drinking beer out of. Grab up a couple while you're at it and take your brewing nerdiness to the next level.