I wasn't quite sure which category this fit into, and if it's not this one, I'm sorry. A couple of friends and I are great friends with our physics teacher. He is a great guy. He likes to use LN2 alot, but to rent a dewar flask is fairly expensive he says and they're not always available. A couple of friends and I are deciding to surprise him at the end of this year with a "you're awesome, thank you" gift at the end of this year. We were planning on getting him a Dewar Flask, about 4 L big. If anyone can help me out in picking out a good quality one for under around 400$ that would be great. Thanks.