Is a thermos type device allowed, i.e. a metal chamber with a vacuum, a Yeti type container, hydro flask, etc??
Yes, however, the container device must: 1) meet every other rule, including the insertion of the beaker and having a 1.5cm unobstructed hole, 2) be altered from its original purchased state by having a substantial modification to it, and 3) Note per rule 3.f. event supervisors may request that the device be disassembled, which would include looking inside any layers of containers, vacuum chambers, etc.