Introduction and 30 oz insulated tumblers

Introduction

    This blog will deal with consumer issues. That's about as specific as it gets. Eventually, I'll discuss how to shop eBay more or less safely and securely. I'll cover specific products, occasionally. The range may expand with time.

   The subject of this page is the thermal tumblers popular with many people and the analysis of their online reputation.
   There is an insulated cup/tumbler made of metal and that comes with a clear plastic lid. The lid has a couple of rubber O-rings to seal the lid in place. There are three major companies in the marketplace:
Yeti
Rtic
Ozark (Walmart)

In surveying the tests run by individuals on YouTube and articles in online magazines, eZines, one comes away with a ranking like the one I just used. These discussions and test are not done by scientists and the results may be correct in the ranking, but the numbers are wrong because the method is wrong. The method is wrong because no one has applied a knowledge of physics and calculus to the analysis.

First.
   The rate of flow of energy is proportional to the difference between the inside and outside temperatures. Running a test on hot coffee in summer will have noticeably different results than hot coffee in winter. If the difference is low, ice will remain longer and coffee will stay hot longer. If the difference is high, ice will melt sooner and coffee will cool more quickly.

Two.
   The plastic lid is a source of thermal leakage. The sipping hole next to the rim allows heat to escape or, in the case of a cold drink, heat to enter. The size and shape of the hole is a determining factor.
The lid is one layer rather than to layers separated by a vacuum.

Three.
   The walls are not of a uniform thickness from top to bottom, therefore the degree of insulation varies from top to bottom. This can be felt by filling a cup to the top of the first level, about four inches from the bottom and swirling hot coffee around. The increase in warmth of the surface of the cup is immediately felt, indicating poor insulation.

   I purchased a 30 oz. Rtic tumbler with lid and purchased a splash proof lid with a rubber plug that seals the lid against thermal leaks as well as spills.
I filled the tumbler with 20 ozs. of very hot coffee and placed the tumbler in one of the side pockets of a backpack. I then took a hike to a general store a couple of miles away on an interstate in mid 40's temperatures. From about 1:30PM to about 6:30PM with a 15 minute stopover in the store.
   I stopped shortly after leaving the store and tasted the coffee. The coffee was still hot but not as hot as when I left. Where the coffee was uncomfortable hot when I filled the tumbler, the coffee had become comfortably hot, but definitely hot. However, when I got back home, the coffee had cooled to the point of being very warm and almost hot.
   The claims that ice will remain in a tumbler after 48 hours remains to be tested, but my expectations are not high. After two days backpacking in the hot sun, I would expect the ice to have long since melted.
   These cups are intended for commutes to and from work for the most part, and in that, they work well. For long hauls like backpacking or interstate travel, a better cup can be found, though more expensive, no doubt.
   I found a problem no-one mentioned. If a spill proof, sealing lid is used, the lid will pop out with a hot drink. The air in the cup is cooler than the coffee. When filled and sealed, the air gradually heats up. But if the cup is agitated, the air will heat up and expand, causing the lid to pop up. Insert the lid and swirl the cup with the stopper out so the inside air can heat up, then place the rubber stopper, and the lid will stay in place.
   There are handle grips made for these type of cups. If one can be found that is wide and covers the upper part of the cup, the insulating value will increase and energy transfer will be slowed down some.
   Another option is to find a foam cover that is frequently found for beer cans and bottles.
   As I said, these are good for a commute or in-office use, but not advisable for long extended travels outdoors.