Just bought a stainless steel 1litre flask for £8.99 from poundstretcher. It has a screw tap which gently releases contents to the air. I'm not sure how it would work in practice, I only fly a cessna !
Boyles law would suggest the air in the flask may increase in pressure as the ambient pressure drops, resulting in a nice hot spray.
I'm not sure about the vacuum in between the layers of the flask. Is it a true vacuum ?