After our recent foray into shirt drying times I thought I’d take a crack at pants as well. Here are the contenders:

  • Prana Stretch Zion ($85, 400g, 97% nylon 3% spandex), the reigning champion of outdoor pants
  • Kuhl Kontra Air ($85, 329g, 72% cotton 26% nylon 2% spandex), a lighter cotton-based alternative that I’ve been evaluating as a replacement for the Zions
  • Urban Star ($15, 744g, 98% cotton 2% spandex), a pair of daily-wear jeans I picked up at Costco
  • Smartwool 150 leggings ($85, 170g, 87% wool 13% nylon), a super-old pair of thermals I found in the back of my gear closet

The jeans and thermals are just to mix things up a bit.

The main question we’re trying to answer: is the drying performance of the mostly-cotton Kuhls so poor compared to the all-synthetic Pranas that I’d be endangering myself by wearing them outside?

Methodology

  • Find some pants
  • Soak them in a sink until they’re fully saturated, kneading them to overcome any DWR (the DWR finish on the Pranas is a real beast)
  • Hang them up to dry
  • Turn on the bathroom fan to get some airflow and keep moisture from building up
  • Take them down and weigh them on irregular intervals (every five minutes at first, then 30 minutes and finally an hour as the drying times slow)

Remember, I’m not a scientist, I’m just some guy hang-drying stuff in his bathroom. I mean, for all you know I’m a brain in a jar with a bad ghost writer who’s never been backpacking (and that’d probably be an improvement, honestly).

Predictions

Based on what we learnt-ed last time here are my predictions:

  • Garments will absorb water in proportion to their weight regardless of fabric composition. This is because the amount of water which can be held by a fabric is primarily dictated by thickness and in the absence of a proper caliper we can use weight as a proxy.
  • Drying rates will be more or less identical across garments. Since drying rates are proportional to surface area and these are all pants of the same size (with the possible exception of the thermals) we expect them to dry at more or less the same rate.
  • Since the Smartwools are half the weight of the Kuhls I would expect them absorb about half as much water and to finish drying much more quickly. The Pranas should be almost indistinguishable from the Kuhls and the Urban Star should be a very distant last place.
  • Garments will dry top-to-bottom and as a garment starts to feel dry it will also dry more slowly. This is because gravity pull water down through the fabric concentrating wetness at the bottom and as the surface dries it no longer contributes to the drying rate (i.e. if 50% of the surface is dry then we would expect the drying rate to be half that of a fully saturated garment).

Results

Here’s the spreadsheet:

https://docs.google.com/spreadsheets/d/1Q4XQYWPoK9tLUSUMtIOGXtkwnUMmvr0h2HTmBEHIx7s/edit?usp=sharing

Water Held

Here’s a graph showing the absolute amount of water held:

Things look more or less as expected – the Urban Star holds a little less than twice as much as the Pranas with the Kuhl right behind. – until we get to the Smartwools. Instead of holding about half the water of the Kuhls they’re close to three quarters. Without a thin pair of woven wool pants (does such a thing exist?) we can only speculate, but my guess is that thermals are much thicker compared to the paper-thin Kuhls and as such hold more water.

Note the slopes of the lines: up until right around six hours the drying rates are constant. Past six hours the Costcos remain straight while the others taper off. I believe this can be explained by the drying rate tapering as the surface of the garment becomes dry – the Costcos were completely wet the entire time whereas the other pants had almost completely dried.

Also note that the Smartwool line is flatter: not only are they holding more water than expected but it looks like they’re drying more slowly as well. We’ll get to that later.

Next, here’s water weight expressed as a percentage of dry weight:

All the garments start out around 100% with the exception of the Smartwool which is about 50% higher. The Costco jeans are incredibly thick yet absorb relatively as much water as the two pairs of hiking pants so I don’t think that thickness alone can explain this one. Does wool really hold that much more water?

Drying Rates

First, here’s how much drying was going on in absolute terms (I’ve omitted the first data point which is incredibly high due to drip-drying and makes the rest of the graph unreadable):

After about an hour in things more or less stabilize, everyone is on a downward slope except the Costco jeans which have a more or less constant drying rate – and also the highest drying rate! Although, this is most likely because they were completely wet for the duration of the experiment while the other garments all reached a relatively dry point.

Second, let’s look at relative drying rates:

Note that the Pranas and the Kuhls are more or less indistinguishable, meaning that from a completely-soaked starting point they will both finish drying at about the same time even though they hold different amounts of water.

Rankings

From a completely-soaked starting point the garments will dry in the following order:

  1. Kuhl Kontra Air
  2. Prana Stretch Zion
  3. Smartwool 150
  4. Costco Urban Star

Note that the only pants that had actually dried completely during the experiment were the Kuhls.

What Does This Mean?

Well, to answer our initial question: if I’m wearing the Kuhls in the mountains and I get them soaked then they’ll actually dry out slightly faster than the Pranas so they’re better not only in terms of weight and breathability but drying as well. However, the difference is so slight as to be of little practical difference. The most important thing is that they aren’t any worse.

The Urban Star jeans didn’t have a single dry spot on them after nine straight hours. Avoid heavy cotton jeans at all costs if becoming wet and cold is a concern.

Finally, the Smartwools are a wildcard. They initially held a lot more water than expected but also dried relatively quicker than all the other garments. I’m not a huge wool guy so, not having anything else to compare them with, I’m at a loss as to why this might be.

Future Work

Waiting around all day for stuff to dry is mind-numbingly boring so I don’t anticipate doing any more of these. However, there is another question which might be interesting: how do the garments perform from the same starting point (say, 100g of water each)? Although getting soaked is definitely one concern when you’re outdoors another is just basic moisture management and when it comes to sweating that happens at a rate that’s independent of how much water your clothing can absorb. So if one garment could dissipate 100g of moisture twice as fast as another then I’d probably rather have that on even if it could hold more water overall. Optimizing for the common case over the worst case, more or less. Of course, if we’ve already established that drying rates are proportional to surface area then we would expect all similarly-sized garments to perform identically. Practically speaking I think it’d be hard to evenly disperse a fixed amount of water uniformly across the surface so I wouldn’t hold my breath for this one.