I am trying to replicate a vacuum flask (on a low budget) with a 1m long 8 inch UPVC pipe forming the outer shell. A search of the internet suggests that the influence of convection stops around 10 Pa, however the vacuum pump I have, a two stage rotary 3 cfm advertised to achieve a vacuum of 2 PA, can only achieve around 350 Pa. My question is, what is the typical vacuum/pressure in a domestic vacuum/Thermos flask and how is it achieved? i.e. a vacuum pump or creating a void in the manufacturing process.