Product Evaluations

64oz Insulated Thermoses – The Buyer’s Guide

Figure 1: How do Thermoses Really Measure Up?

Abstract: It seems that every outdoor gear supplier and general store has their own version of insulated thermoses.  These products are used in every aspect of outdoor activities whether you are camping, hiking, fishing, hunting, mountaineering, etc. Most people are familiar with some of the big name, high dollar products such as YETI and Hydroflask but how do they really measure up to their more economical competition such as Guidesman and Ozark?  True North Engineering Testing set up this simple test to unveil the scientific truth behind who really keeps your coffee the warmest and your beer the coldest, the longest. Enjoy and please drink scientifically.

Executive Summary: While measuring the thermal decay of a temperature gradient for similar 64 oz. thermoses, the Ozark and YETI brands yielded similar performance while clearly outperforming the Hydro Flask and Guidesman thermoses.  The following table and figure show the thermal decay of boiling water for the first 3 days sitting in an approximate ambient temperature of 40 degrees Fahrenheit.  Perhaps the most crucial time frame is the first 24 hours in which the Ozark and YETI brands kept the water 30-40 degrees hotter than the Hydro Flask or Guidesman thermoses.  That is the difference between hot and lukewarm Coffee at camp!

Figure 2: Thermal Decay Recorded Data – First Three Days
Table 1: Thermal Decay Tabular Data – First Three Days

General Test Procedure:

  1. Four test specimens were independently and randomly procured.  Two of the specimens are known to be “higher end” brand names while two specimens are known to be “economical” name brands.
  2. Thermocouples with light gauge wires were adhered to the interior thermos floors and walls and ran out of the thermos allowing the manufacture gasket to maintain its seal.
  3. All test specimens were pre-warmed for 15 minutes with boiling water.
  4. All test specimens were re-filled with boiling water then immediately sealed and placed in an environmental chamber to sit until an ambient temperature of ~40˚F was reached in each specimen.
Figure 3: Test Setup

Analysis of Data: When strictly evaluating the data, the design of the Ozark and Yeti insulated thermoses are superior to the designs of the Hydroflask and Guidesman insulated thermoses.  It was observed that one large difference in design between the two higher performing products in comparison to the two lower performing products was the lid style.  The Yeti and the Ozark lids have a plug design that makes its seal at the inner wall of the insulated thermos which appeared to be a superior design compared to the Guidesman and Hydroflask design. The Guidesman and Hydroflask design have more of a cap style lid that seals the thermos at the outer wall of the insulated thermos. It appears that the important take away is to observe the style of lid when choosing your next thermos.

Figure 4: Difference in Lid Styles Correlated to Performance
Figure 5: Thermal Decay Recorder Data – Ten Days

General Comment: Note that the intent of this test was to perform a quantitative comparison of the insulation properties to determine how the four competitive products perform for what they are designed to do.  There are many other factors that were not evaluated which can drive a personal preference such as color choice(s), vendor customer support, name brands, impact resistance, etc. that may factor into a person’s decision as to what product to purchase.  This test report is simply intended to provide scientific data to the outdoor community to help them make better choices on which consumer products to invest and rely on.