Most lids you've ever used have pressure relief. It's not an extra part or valve or anything, it's just the simple geometry to ensure that the seal opens before the lid becomes mechanically free.
Most lids you've ever used have pressure relief. It's not an extra part or valve or anything, it's just the simple geometry to ensure that the seal opens before the lid becomes mechanically free.
Thermos has only been producing flasks since 1904. There shouldn't be an expectation that they already have this on a checklist of things to watch out for in new designs. /s