Water Retention In Clothing

Part of Recommended Outdoor Gear by Mark Verber

Very early draft.

When in the back country it is important to manage moisture. Nothing will chill you faster than wet clothing. On extended trips it's necessary to be able to dry clothing over night.  So you want clothing that dries quickly and keeps water away from your skin. There are several factors that effect water retention in clothing. I would recommend reading the BPL thread about water absorption in textiles which I participated in, but there were people with more knowledge who contributed their thoughts.

My experience is that water retention (called regain in the industry) is driven by three inter-related issues. The base material, the fiber (how the material is assembled into fabric), and the thickness of the fabric. For example, even though nylon absorbs 2x more water than polyester, a thin nylon woven shirt (like light weight supplex) can have the same water retention / drying properties as a knit polyster base.

Over the years I have read people talk about how much water various materials absorb. Most of the time the numbers seemed low, so I ran some simple tests to determine how much water was absorbed by various garments that I use (which is a combination of material, fiber, and weight/thickness). Alas, I have misplaced the spreadsheet with all the results.  So the following data is (1) possibly wrong because I don't have a great memory (2) wasn't super rigorous (3) wasn't a pure apples to apples test.  I didn't use the same weight for each material.  Rather I used the shirts I owned. The specific shirts I remember included:

Polyester: light weight powerdry
Polypro: light weight base layer (20 years old or so)
Cotton: Haines beefy-tee with a logo from my work
supplex nylon: RailRider Eco Mesh
wool: smartwool light weight tee
rayon: aloha button up shirt
bluesmith hydrophobic shirt (polyester+nanospheres)

First Test: Weight the garment, submerged it under water and kneaded it, pull it out dripping wet, weight it, squeeze everything out I could get out, weight again, wear for 30 minutes, weight again. Something that was pretty surprising is that when I did this test, the dripping weight was much higher than I expected. with the exception of the bluesmith shirt which was only 1.2x, nearly everything was at least 2x, wool being 3x, cotton 4x, and rayon 5x. After 30 minutes of wear, the figure were something like bluesmith 1.05x, polypro 1.2x, supplex 1.3x, polyester 1.3x, wool 2x, cotton was 2.5x. Not as large a difference as I would have expected.

Second Test: I concluded that the kneading the item fully submerged wasn't a good test. It was most likely measuring void space in the garment and how easy a super saturated garment would release moisture rather than what it would absorb so I tried what I though was a more "reasonable" simulation. The real life situation I was wondering about was what would happen to my base layer after my windshirt fully wet out... how much water would be absorbed and how quickly would it dry out. The second experiment's steps were:

  1. Weight the garment
  2. Placed it on top of a sink filled with water
  3. Briefly pressed it into the water repeatably for 30 minutes
  4. Shake item. Weight
  5. Squeeze. Wear 30 minutes. Weight

When I did this the number were significantly different. Polypro and polyester were less than 1.1x gain after the shake, and more or less completely dry after 30 minutes. Nylon was 2x gain after the shake, and about 1.1x weight after 30 minutes. Wool and acrylic were something like 2.5x after shake, and around 2x after 30 minutes. Cotton was 4x after the shake, 2.5x after the squeeze, and 2.4x after 30 minutes of wear. I am pretty hazy on the acrylic and rayon. My memory was the acrylic was around wool, and the rayon was worse than cotton after the squeeze, but had already surpassed cotton after 30 minutes of wearing. After one hour of wearing I hung the clothing in a location that the temp ranged between 45-50F with a relative humidity of approx 70%. Eight hours later then cotton shirt still felt wet. The wool was still damp, but reasonably comfortable.Everythng else was comfortably dry.

 My personal conclusions were the that polyster / polypro didn't absorb a lot of water. Supplex absorbed more, but was sufficiently thin without voids so it dried quickly. I was unimpressed with wool. Cotton really sucks because not only does it suck up the water, but it didn't want to let go.  This more or less matched my experience in the field.

The backpackinglight.com folks did a more rigorous field test: comfort moisture transport in wool and synthetic clothing. They found that wool took 50% longer to dry than polyester. My personal experience was that it takes longer than that, but we were using different fabrics and fabric weights than what I was using, and I believe invested more effort into having a true apples to apples comparision,

The champ will likely be nanotech clothing fabric.



There is some very sophisticated science being applied to clothing material. Examples include Schoeller's nanospheres which virtually clean itself, a treatment from Avelana and Roudiere which is first being applied to wool which has some thermoregulation properties much like Outlast, several Japanese companies are making garments that generate heat when they get wet, materials which are normally soft but stiffed to provide protection during an impact developed by d3o, and clothing as a battery. Some folks are claiming that high concentrations of some metals speeds recovery time which I am somewhat skeptical of. There is also a trend toward mixing different materials using tools like thermal mapping to guide the level of insulation, moisture transfer characteristics, etc to different parts of the body. There was an interesting article comparing Sir Hillary's Clothing on Everest to what we wear today. While this comparison is interesting, his system wouldn't fair as well against a more careful selection of modern clothing. There was an interesting thread about Clothing Science and Folklore on backpacking.net. There is a classic article called General Principles Governing vSelection of Clothing for Cold Climates by Paul Siple of the U.S. Army from 1951 which provides useful background information. Many of Richard Nisley's postings on BPL are filled with useful, science based information.

FabricLink has a decent index of high performance materials and Keith Conover wrote up his experiences with different clothing materials. The US military has spent a lot of time and money working on clothing materials. You also might be interested to look at a discussion about the performance characteristics of the new protective combat uniform and a review of the PCU.