[vmelkon]

With the temps that low, I cant imagin it making a world of difference. A Dewar flask has a vacuum between the inside and outside, NOT insulation (it attempts to stop thermal conductivity between the liquid and the rest of the world) Now, some thermoses per wikipedia use this technology (apparently the expensive Thermos brand ones) but I cant imagine the vacuum being as strong as say, a professional one.

Good point. I have broken one and the glass thickness is 2 mm. Perhaps it doesn't have a total vaccum in it.
I'm not sure about the distance between the glass walls but I estimate less than 1 cm but perhaps this isn't important.

[408]

I have a 4L glass dewar at home, kind of in the style of a large round bottom flask to minimize surface area.  Real dewar, not improvised.  When in the past I have brought LN2 home, with a styrofoam cork in the dewar, I had usable LN2 for 3 days.

I just moved, now I can post from home again