Do Triple-Wall Bottles Really Have Better Insulation than Dual-Wall Bottles?
You’ve probably heard about dual-wall insulated bottles, but what about triple-wall? If two walls are good, then three are better, right? Let’s find out.
Dual-wall stainless-steel bottles have been around for a long time, and brands like Hydro Flask and YETI really launched them into mainstream use within the last decade. Each bottle has two walls of stainless steel with a vacuum in between, and the lack of air reduces how much heat can transfer in or out. We tested quite a few of these bottles for a video earlier this year, and that turned into one of our best-performing posts.
Triple wall bottles are not as widespread, but there are a few brands out there marketing this type of design, including S’well, RevoMax, EcoVessel, and Owala. We didn’t discuss this type of bottle as we would have liked in our previous insulation test video, so we thought now would be a good time to revisit it, this time with a focus on seeing if the triple-wall design is worth the marketing hype.
Here's what we'll cover in case you'd like to skip ahead to a certain point.
Our Video Review
Our YouTube video covers the same information in this post, so click the link if you'd rather see the video. Otherwise, keep reading the full post below!
Before we get started, there are a few details to point out.
"Triple-Wall" vs "Triple-Layer"
Many people assume triple-wall means three walls of stainless-steel, but that’s not correct. If you look closely at the marketing and listings, you’ll notice that it probably says “triple-layer” instead of “triple-wall.” It’s a small but significant distinction because they don’t really have three walls. They have the same dual wall construction with a vacuum in between, and the third layer refers to a copper coating on one of the stainless-steel walls.
From S'well's website:
“Thanks to our Therma-S'well® Technology and triple-layered insulation, which includes a copper layer, S'well products are able to keep any liquid hot or cold for long stretches, while maintaining a condensation-free exterior.”
You might be wondering how this would help. Copper is known for being a good electrical conductor, but it also has a high thermal conductivity. This means that heat is transferred very easily through it, so why would a copper layer help bottle insulation?
How Triple-Wall Bottles Limit Radiation Heat Transfer
The key difference with radiation compared to either conduction or convection is that radiation does not need matter to transfer heat, which allows for radiation heat loss through the vacuum in dual wall bottles.
Emissivity: How Different Materials Allow Radiation Heat Transfer at Different Rates
Emissivity is a material property that indicates how efficiently heat is transferred by radiation. A material with a lower emissivity value will transfer less radiant heat compared to a material with a higher value. Copper has an emissivity of 0.05, so while the copper coating won’t do much to prevent heat conduction, it will help prevent heat radiation. For reference, stainless-steel has a higher emissivity of 0.59, so the steel won’t prevent radiation heat loss as efficiently by itself.
So that’s the science behind the triple-layer and how it theoretically is better, but how does this translate into actual results and is it significant enough of a difference for you to consider when buying a bottle? Let’s find out!
Insulation Test A (Using a Uniform Styrofoam Cap)
We looked at 14 total bottles. 11 bottles are dual-wall, and 3 have triple-layer insulation with the copper coating.
We were originally going to boil water to recreate steeping tea or brewing coffee, but it would have taken quite a few batches and taken a lot longer. So instead, we filled up each bottle with the hottest water from our sink.
As mentioned before, different lids have different insulating properties. Because our main goal was to compare the triple-layer vs dual-wall insulation, we wanted to keep the different lid styles from impacting the results as much as possible. We purchased a sheet of Styrofoam insulation, cut it into a bunch of smaller pieces, and pressed them onto the rim of the bottles. This created an impression in the Styrofoam pieces that helped limit the potential for gaps and temperature loss.
We poked a hole through each piece of foam with our thermometer, and we used a few other smaller pieces of insulation to cover up the holes when we weren’t taking measurements.
Test A Results
We measured the temperature every hour for the next four hours, again around hour 8, and one more time around hour 20. With each measurement, we inserted the thermometer through the hole in the Styrofoam cap until the temperature equalized.
This chart and graph show the percentage temperature change at different times during our test, which lasted 19 hours and 31 minutes. Temperature drops ranged between 17.2% on the low end to 27.0% on the high end. Looking closer at the data, there are a few interesting results to note.
Two of the triple-layer bottles, RevoMax and S’well, had the best results. The third triple-layer bottle, EcoVessel, didn’t fare as well, but it was still in the top five.
The best dual-wall bottle really surprised us. Ozark Trail, the Walmart brand bottle that we bought for $11, had an 18.5% temperature loss. Compare that to 20.9% for a $50 YETI Rambler and 24.2% for a $45 Hydro Flask.
The worst bottle by a wide margin is Steepware, which is a bit ironic given that it’s primarily made for brewing tea. That being said, it’s probably not a major concern because most people will drink the tea within a few hours before it goes stale.
So based on the results, it does appear that the copper layer may have an impact and helps insulation. However, depending on which brands you’re comparing, the difference between triple layer and dual wall insulation might not be as great as you would have thought. When you average the percent temperature loss for dual wall vs triple layer bottles, you get 22.7% and 18.3% respectively. A 5% difference over 20 hours is significant, but it’s not really game-changing in our opinion.
However, there’s another big variable that makes this conclusion a bit uncertain. We can’t afford to buy every type of bottle, and it just so happens with our bottle collection that the two best performing bottles were also our only two narrow mouth bottles. Because most heat is lost through the lid and mouth opening, narrow mouth bottles should have an advantage over wide mouth ones. We’d like to do another test in the future that focuses on wide-mouth vs narrow-mouth insulation once we have more narrow mouth bottles to compare.
Insulation Test B (Using the Manufacturer's Lid)
But let’s face it, you’re not going to be walking around with one of these bottles with a Styrofoam cap. We did the test first because we wanted to isolate the effect that the copper layer has on the insulation, but the more practical test that you can use compares the bottles when using the lids that they come with. So we ran a 2nd version of the test using the bottle lids.
For each measurement, we swapped the bottle lid with the Styrofoam piece from the previous test. Then we pushed the thermometer through the Styrofoam, and this prevented excessive temperature loss for the 15-20 seconds that we needed for each measurement. Once we had the reading, we put the normal cap back on.
Test B Results
This test lasted for 19 hours and 17 minutes, and we made the same type of chart and table to show the results. Right away, there are some interesting data points and details to unpack.
The relative rankings were mostly the same as with Test A, but there was a much wider range of results with a 13.5% temperature drop on the low end to 30.1% on the high end. That’s an increase in the range of results from 9.8% with Test A to 16.6% with Test B.
The same two brands performed the best (RevoMax and S'well), but they widened their lead significantly. However, keep in mind that these are the only two narrow-mouth bottles in our test.
Ozark Trail had a great showing again, and this was the best dual-wall bottle in both tests.
Unfortunately for Steepware, this bottle was even more of an outlier on the wrong side of the average compared to Test A.
Does the Bottle Manufacturer's Lid Help Insulation?
While the relative rankings were similar for both tests, you may have noticed the rankings did change in some cases. For example, Hydro Flask’s Trail Series jumped from the 2nd worst with Test A to the middle of the pack with Test B. Since the only change between the two tests was that we switched from the standardized foam pieces to each brand’s lid, any changes in the rankings means that some brands have designed lids with better insulation than others.
Standardizing the Results
Tests A and B had slightly different total durations, so to better illustrate how the results for each bottle changed between the tests, we needed to standardize the results. We calculated the temperature drop per minute over the duration of both tests, then we multiplied that by 1200 to simulate a 20-hour test. Then we compared Test A vs Test B for each brand, and this graph shows how each brand changed.
Bottles that fall on the left side had better results with their brand’s lids instead of the Styrofoam cap, and bottles on the right did better with the Styrofoam.
S’well, RevoMax, and both Hydro Flasks were the only bottles that improved with Test B. When you look at the lids with each of these bottles, you can see that they seem to have more built-in insulation, like with S'well and RevoMax.
Most of the other bottle lids like Steepware and Takeya don’t have built-in insulation and just have single layer plastic construction in the cap, so it’s understandable that they didn’t fare as well.
Conclusions: Are Triple-Wall Bottles Worth the Hype?
So when we take a step back and look at the results as a whole, we have a few main takeaways.
Based on these results, we have a few more video ideas that we may work on in the near future. Once we have more narrow-mouth bottles in our collection, we want to compare those against wide-mouth bottles. We also think it would be interesting to focus on premium brands vs budget brands, because let’s face it, we’re probably not the only ones that were surprised that Ozark Trail outperformed YETI. And finally, we only ran one instance of each test, and for more reliable comparisons and data, we ideally would repeat the test more times and average the results.
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