By The Numbers: How Bad is Thermal Degradation in Synthetic Insulation?
Jul 6, 2021 at 9:00 am #3721107
Companion forum thread to: By The Numbers: How Bad is Thermal Degradation in Synthetic Insulation?
The latest findings on thermal degradation in synthetic insulation from Stephen Seeber may surprise you in this By The Numbers column.Jul 6, 2021 at 11:08 pm #3721165Ryan JordanAdmin
@ryanLocale: Central Rockies
Well done. Critical skill to learn as a ULer: be intentional and take care of your gear.Jul 7, 2021 at 7:33 am #3721198Jeff McWilliamsBPL Member
Beginner backpackers buy synthetic or cheap down bags (like the Kelty Cosmic 20 down bag). When they realize the bag takes up a lot of room, they run out to REI or whatever and buy a compression stuff sack, and smash that sleeping bag down into the smallest cylinder they possibly can.
Often the same practice is used with their clothes.
I’d like to see this simulated in a test like this, because I don’t feel like the washing machine test is representative of this practice. (And the article more or less admits this is the case. )
Nice article. Demonstrates that taking good care of your gear will result in less degradation, and that Primaloft has improved their product over time, which is good to know.Jul 7, 2021 at 8:05 am #3721203
Thanks for doing this. Takes a lot of work to do these types of experiments.
It seems like it wouldn’t be that difficult to manually do a quantitative compression test. Have a cylinder, your pillows, weight on top, like Ryan’s test. Put the weight on for a period of time, take it off for a period of time, repeat. Maybe 1 minute of your time per cycle. 24 hours per cycle to simulate actual usage.
Maybe you need a bigger weight than the 5 pounds that Ryan used. Manually compress as you would if you were compressing in your pack and see how much it compresses. Then find a weight that compresses the same amount for your test.
That’s a reasonable conclusion that the insulation used years ago was different and more susceptible to compression damage. I like it when established knowledge (synthetic insulation is susceptible to compression damage) is challenged with experiment and data.Jul 7, 2021 at 5:30 pm #3721249
Jeff and Jerry:
Thanks for your comments.
First, I think it may take more than an article I write to change the behavior of first time buyers and beginners. But, at least I can get information out and hope it spreads.
Ironically, I received the first insulation I hoped to test. It was packaged in such a way that it is permanently damaged! Too much compression. Areas lost 50% or more of loft. Fibers are permanently creased. First data point on failure due to compression. Don’t know the forces used to wreck the insulation, but it does prove that high compression will destroy the insulation, just like Ryan said in his video.
It is unclear whether compression beyond a certain pressure (PSI) will cause damage (from our first data point, seems like it will) or cyclical compression will cause damage or cyclical compression beyond a certain PSI will cause damage. Bear in mind that simply measuring loss of loft is insufficient. First, small changes in loft are very difficult to measure accurately. That is particularly true for batt insulation. Second, the relationship between loss of loft and loss of thermal performance is not linear. We are really concerned with loss of thermal performance, so that is what has to be measured. We know, from my first paper in the insulation series, that thermal performance within even a yard of insulation is inconsistent. This has important implications for how I run the test. The thermal performance of each sample must be measured at each stage of testing. The test must be conducted so that compression force per square inch is quantified. Quantification, potentially, will allow different insulations to be compared. I started this process with a fairly easy test that is widely used in the industry for measuring insulation degradation–laundering. The next iteration will deal only with compression force. This is how I anticipate doing this: I will cut four insulation samples for each 6 osy Primaloft and Apex. They will be cut to fit my guarded hot plate. Thermal resistance of each will be measured. Next, concrete pavers will be cut to cover the insulation sample. This will require 20 pavers. One layer of pavers will approximate the psi imposed on sleeping bag insulation by a typical male adult. I will weight each sample with 1, 2, 3 or 4 layers of pavers. I will leave the pavers on the samples for 24 hours. I will remeasure thermal performance of each. Then-who knows, it depends on the results. The results of this test may inform a useful test for cyclical loading.
This is the least expensive concept I can come up with, so far. Of course, we don’t know if what we find for 6 osy insulation will apply to 3 osy insulation or 10 osy insulation. Nor will we know how it applies to other brands of insulations. There is going to be a limit to what can be known and how to turn this into actionable information for the end user. I suspect it will end with advice to be very careful when compressing your synthetic bags and garments, just like the current article. But, we shall see where this leads and what can be learned.
As it happens, a friend of mine is going backpacking. He was lamenting that his sleeping bag, using the stuff sack it came with, does not fit horizontally into his pack. He was planning on going to REI to purchase a compression sack. He is a big, strong guy. I am betting he will get it to fit.
Now, if any of you want to weigh in on alternatives, I am happy to consider them. If anyone has clever and low cost methods for measuring batt thickness, I am happy to hear that too. I have come up with several methods. None are totally satisfactory. I can think of some methods that would probably work well, but the instrumentation would be complex and/or too expensive.Jul 7, 2021 at 9:00 pm #3721308
when you say 1 paver approximates the pressure from an adult male, you mean compressing it to fit into a pack? then maybe that’s as much pressure as you need for testing?
and then maybe putting 1 paver on for 24 hours, then test to see if R value is degraded, then repeat a number of times to simulate what would happen is real use
just brainstorming here : )Jul 7, 2021 at 9:42 pm #3721314
This test is about steady state compression. Not cyclic compression from stuffing a sleeping bag into a sack. That may come later. This test will identify how much force is required to degrade the insulation so that its thermal resistance is permanently reduced.
The weight of the paver, per square inch, is close to the weight, per square inch of a typical male lying on his back or front, in a sleeping bag, applies to the insulation in the bag.
Basically, I will stack more pavers until the R-value begins to decline.
“Real Use” might be difficult to replicate. I think that might depend upon how determined one is to get a sleeping bag to fit into a particularly small compression sack. One step at a time on this.Jul 8, 2021 at 7:16 am #3721320
ahhh… that makes sense
great projectJul 11, 2021 at 9:41 am #3721649Michael RayBPL Member
Small typo at beginning: “Experience suggests that down garments will have a longer life expectancy than their down counterparts” (second “down” should be “synthetic”)Jul 11, 2021 at 9:53 am #3721650
Yes. I noticed that this morning too. Palm of hand to forehead.
I will send a note and see if that can be corrected.
Thanks for reading.Jul 11, 2021 at 11:31 am #3721656Tim HawthorneBPL Member
Nice article. The problem with synthetics is constantly compressing them more than washing them. I have good synthetics many years old that I always pack loosely. I use them to “fill up” the remaining volume of my pack. Never use a tight stuff sack!Jul 11, 2021 at 3:09 pm #3721669Rob St. JohnBPL Member
@robstjohnLocale: American Intermountain West
Regarding Tim Hawthorne’s comments on stuff sacks. Maybe it is just my experience but it seems vendors prize themselves on the bragging rights of just how small an item can be compressed into a stuff sack, e.g. “smaller than a 1 liter water bottle.”. Personally, I find it aggravating, as well as detrimental to the item, to negotiate the Herculean task of stuffing items back into their OEM stuff sacks. Most of the time I find it necessary, at least for my own sanity, to replace the OEM stuff sack with one that is more practical. Besides, if it needs to be compressed more it, that will most likely occur as your pack fills up.
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