There is a click bait video circulating right now that makes some bold claims about down being hydrophobic. I think most people with ample experience with down stuff can see through this sort of misleading information, but it uses some real shock value testing that catches people who maybe don’t quite understand what is going on. In all fairness, I don’t know that the video was created through nefarious means. It was likely created with good intentions, but just a poor understanding of down and down construction.
Down is, of course, quite hydrophilic. A plume will readily soak up water and lose loft. However, when you put a bunch of it in a chamber, it actually becomes pretty difficult to get it wet in an isolated incident. All that air trapped inside the chamber keeps water from entering through the shell unless forced through. So you can repeatedly dunk down items into water, submerge them, and swish them around, but basically only get the outer shells wet. The shock value is in that it looks wet, feels wet, and you can weigh it to confirm moisture was absorbed…..but the down inside the chamber is totally dry. What happens is water absorbs into the shells and a little bit of the top surface of down. The inner loft stays totally dry. Anyone who has ever washed a down item knows that it doesn’t really get wet until you submerge it and squeeze all the air out. Without doing this, you can dunk and dunk and dunk, but the down stays dry and lofty.
So, in short, isolated events, down is pretty difficult to get wet. This is not, and has never been the risk to down gear though. The problem with down is that, on a material basis, it is quite hydrophilic. So, you can dunk a chamber and the air inside will keep the inner parts dry, but the outer down that is in contact with the wet shell will slowly absorb the water. If that shell stays wet for long periods of time, then the down will continually absorb more and more and lose more and more loft. This scenario is most likely with down garments if the wearer isn’t careful about keeping it out of precipitation. They might get the shell wet and then pack the garment up when they’re done, only to find that the wet shell transferred all that moisture into the down and the loft is flat. For sleep systems, the typical risk is long term accumulation of internal condensation. A sleeper puts off moisture through the night as they sleep. In warm temperatures that moisture pushes all the way through the system and out. However, in cooler temps, there is often a dew point within the down of the sleep system and the moisture will condense there. The effects of this can be apparent after just one night if the conditions are right. If those conditions continue to exist night after night, then more and more loft will collapse as more and more moisture is absorbed. The tricky thing about this issue is that it doesn’t always happen. It really depends on where the dew point is along the temperature gradient. If the person is putting off a lot of heat, then the dew point will likely be outside of the system. If the system is under-insulated, then the person’s body heat is likely to be enough to put the dew point outside. Different people put off different amounts of moisture. A person who doesn’t put off much, might not see a significant amount of build up. In arid place with very low humidity, the effects of build up might not become a problem because of how quickly it evaporates away in the morning. However, there are thousands of cases, going back decades, where conditions are such that internal build up is a major, major issue and the mechanisms are well understood. The solutions have always been to stop the moisture going out, or move the position of the dew point by adding layers above that collect and remove the accumulated moisture (overbags / overquilts).
So, while dunking your down gear into a creek has a lot of shock value and might make people think that down is super hydrophobic, it’s just not a good depiction of what the real moisture risks are to down. Don’t fall for it.
Be careful trying to uphold scientific rigor when showing a fundamental misunderstanding of what hydrophobic and hydrophilic means.
I thought I was….
“Hydrophilic – having a tendency to mix with, dissolve in, or be wetted by water.”
A plume of down is very easily wetted. Water readily absorbs into the structure and material.
“Hydrophobic – tending to repel or fail to mix with water.”
A chamber of lofted down tends to repel water. Water does not easily mix into it.
Those seem to fit well, but I don’t claim to be “upholding scientific rigors”. I am a builder, with a specialty in down work, and this is clearly not a controlled lab setting. If you have suggestions for better terminology, let me know.
Since there was no reply, I’ll take a guess at what the criticism is here. In many scientific settings, I imagine these terms are strictly referring to how a substance interacts with hydrogen bonds on a molecular level. I think this is applicable in my calling a plume hydrophilic. However, calling a chamber hydrophobic, when it’s made up of something hydrophilic on a molecular level, is using a more general definition of hydrophobic that maybe isn’t specific enough in a scientific setting.