Which vacuum flask stays hot the longest?

Review of 1 pint (0.5L) vacuum flasks

We put boiling water in vacuum flasks from a wide range of manufacturers, left them for several hours and then measured the temperature. The winner was Zojirushi SV-GG50-XA followed a close second by Thermos Ultimate Insulation.

Results

Temperature of the water from boiling after 8 hours:

Zojirushi SV-GG50-XA	172 F	78 C
Thermos Ultimate Insulation	171 F	77.5 C
LaPlaya High Performance	168 F	75.5 C
Alfi isoTherm Eco	167 F	75 C
Aladdin Fundamentals	167 F	75 C
Primus C&H Vacuum Bottle	166 F	74.5 C
Stanley Classic	163 F	73 C
Emsa Senator	161 F	71.5 C

Smaller flasks normally get cold more rapidly because they have more surface area to volume, so the flasks we tested were all 1 pint (0.5L) capacity. We warmed the flasks with boiling water, emptied them, filled them with boiling water, and left them in a room at 59 F (15 C) for 8 hours. All of these flasks are stainless steel.

Zojirushi

This is an elegant, compact flask with a non-stick lining. Unfortunately, like all the flasks we tested except the Primus C&H flask, it is not dishwasher safe. Manufactured in Thailand for the Japanese company Zojirushi.

Thermos Ultimate Insulation

The Thermos is made in Malaysia for Pacific Market International and comes with a 5 year warranty.

LaPlaya High Performance

Alfi isoTherm Eco

Made in China. 2 year garantee.

Aladdin Fundamentals

Made for Pacific Market International.

Primus C&H Vacuum Bottle

This was the only dishwasher-proof flask in the test. It is made in China. There are two stoppers - one to pour the contents without unscrewing the stopper and the other for better insulation. We tested it with the better insulation stopper.

Stanley Classic

This flask has a large cup and a 25 year guarantee. Made in China.

Emsa Senator

We had high hopes for this sturdy and good looking flask, but sadly it did not retain the heat well. Made in Germany and comes with a 5 year garantee.