Product variations: 

Invented in the early 1870s by physics and chemistry professor Adolf Ferdinand Weinhold, this was the first thermos container to store low-boiling liquids as found with liquefied gases. Weinhold's design was a two-walled concentric transparent cylinder ring which was evacuated, thus practically eliminating heat transport by convection of remaining air. His design was later modified and thereby improved by Dewar who had the cylinder walls silvered, reducing heat flow through radiation, in addition to convection. This design is now universally known as D e w a r  f l a s k. However, the Weinhold design, through its transparency,  still has its applications if a cold liquid needs to be monitored or irradiated. The Weinhold vessel offered by Nordlandglas has three walls, thus considerably lowering heat exchange compared to the the two-wall design, while still being transparent. It has been used for photochemical reactions at -78°C with a sunlamp.