Yes, it’s insulated stainless steele, so you could say it is a thermos. It’s meant to keep things cold or hot for a length of time, and it does. Plastics would not be able to do that. I got the wide mouth lid with a straw for mine and really like it.
Kind of like a thermos. It is the best! After I got this one I also went back and bought the smaller one in red. Loe both of them. They keep tis cold for at least12 hours. The handle is also great and you can buy a top with a str for it too. Enjoy