Lining your pockets: which material makes the best pocket bag?

Thank you for reading the inaugural article of the Proceedings of the Ferrous Mollusk, a scientific leaning non-peer reviewed blog post that focuses on clothing materials questions. This is written in a way that I would expect if a scientific journal had a baby with a blog. That is for our sakes to make it informative while also being readable and, hopefully, interesting. I would also like to add the caveat that I have only included the simple statistics for the described comparisons. There will be a central question that will be introduced followed by a few experiments that culminate in a discussion to talk about what it all means. The results should be unbiased, but the discussion will be an interpretation of the results.

I have often wondered, of the things that I buy, how much thought gets put into features that are hidden. Unfortunately, it seems like, for most things, that there isn’t much thought beyond “that is good enough” or “who will notice.” This is understandable for low-cost items that are largely disposable. However, for things that I want to keep for years, I want every detail, no matter how visible, to be an intentional decision. That is what brings me to today’s article of the Proceedings of the Ferrous Mollusk. The next chapter of the Tale of the Iron Snail is being written as we speak, and that is a yet to be released pair of selvedge denim jeans. Since you are reading this, you likely know that each chapter of the Iron Snail is a release of a new garment (so far, the Prologue denim jacket and the Mammoth woolen jacket). You may be thinking that the only decision that needs to be made for jeans is what denim to use, but there are some other, often overlooked features like the cut, wash, rivets vs bar tacks, or pocket decoration. However, the feature that I am focusing on is the material for the lining of the front pockets, usually called the pocket bags. Specifically, I will quantitatively assess seven candidate fabrics made of either cotton or hemp for their ability to resist punctures, abrasion, and tearing to identify the optimal material for pocket bags in the next chapter of the Tale of the Iron Snail.

Of the seven candidates, four of them are made from varying types and staple lengths of cotton (see article of the importance of staple length here). 

1. The first candidate is one that you are likely familiar with and will be used as a reference for the pocket bags found in the mass-produced jeans (closest fabric I could find to Walmart jeans) with an approximate weight of 4.5 ounce per yard squared, herein referred to as “George” (figure 1a).
2. The second contender is an upgraded version of the standard fabric, still made of cotton that is plain woven with a weight of 6 ounces per yard squared, herein referred to as “plain cotton 6” (figure 1b). 
3. The third contender is an 8 ounce per yard squared twill woven fabric that is densely woven and made of the long staple supima cotton, referred to “twill supima 8” (figure 1c). 
4. The final cotton contender is a densely woven, but thin, rip stop fabric (woven to include thick threads for a defined number of thinner threads that is meant to stop any rips that may occur) weighing in at 10 ounces per yard, referred to as “rip-stop cotton 10” (figure 1d). 

The remaining three candidates are made of hemp bast fiber. Hemp as a fiber has gotten some bad publicity over the years, just because of some side effects of the leaves and flowers (I will leave it at that). However, the remainder of the plant, including its stalks, can be used to make long bast fiber threads that can be woven into a smooth fabric (trust me, the process is fascinating). 

1. The first contender is the closest comparison to George or plain cotton 6 as it is but is instead hemp that is plain-woven weighing in at 5.9 ounces per yard squared, referred to as “plain hemp 5.9” (figure 2a). 
2. The second hemp fabric has a beautiful jacquard weave that has a combination of thinner and thicker threads giving it a basket weave like pattern, referred to as “jacquard hemp 9.9” (figure 2b). 
3. The final hemp fabric is a plain-woven beast that is substantially thicker than all the other fabrics, begging the question of if it is too thick. Either way, this fabric weighing in at 11.5 ounces, referred to as “plain hemp 11.5? (figure 2c).

Results

Puncture resistance

I would predict the major failure a pocket bag can have is through the formation of holes (I’m still haunted by the polar express to this day, how can you lose that bell?). I do not think it would be farfetched to have the contents of a pocket (be it a pen, keys, or an opened pocket knife) to force a hole after an awkward motion. Therefore, my first test is to measure the force required to poke a hole in each fabric. 

To make this measurement, I stretched each contending fabric and secured each end. I then pressed the force meter cone shape point into the fabric until it broke through, and the largest force for each puncture was recorded (figure 3). In doing this I found that the worst performing fabric was the George fabric (Figure 3A, 3B), which is not surprising since it is our baseline. What was more surprising is that the rest of the cotton fabrics (Figure 3A-3E) did not perform much better than George with the rip-stop cotton 10 (Figure 3E) performing the best (however it isn’t a significant increase). Each hemp fabric (Figure 3F-3H), on the other hand, performed significantly better (P-value at least <.001, T-test) than each cotton fabric where the Jacquard Hemp 9.9 and the plain hemp 11.5 far exceeding any other fabric tested (Figure 3A) Further, the puncture holes in the hemp fabrics (Figures 3F-3H) appear to not have broken the fibers like what is seen in cotton (Figures 3A-3E), which likely is a contributing factor for how the tighter woven Jacquard Hemp 9.9 and the plain hemp 11.5 are able to resist punctures as compared to the looser weave of plain hemp 5.9.

Abrasion resistance

Another way a hole can form is through general wear and tear of the pocket bag, or abrasion. This is especially important since every time we take a step, or move, the pocket contents rub against the fabric to slowly removes some material until a hole forms. Therefore, a desired attribute for the pocket bag is to be as resistant to abrasion as possible. The industry standard is to use a Wyzenbeek double-rub test (oh my) machine that imitates a finger rubbing the cloth until it fails. I, however, do not have one of these machines, so I will have to come up with something different. 

To measure abrasion resistance, I first turned to my orbital sander (a sander that moves the sandpaper in small circles) with a 100 grit sandpaper. However, this strategy was not ideal as what ended up happening was that my test piece of fabric was stretching with the motion of the sander instead of the sandpaper moving across it, as would be expected for an abrasive force. I then turned to an alternate method where I used a 1/2 inch diameter aluminum oxide grinding wheel attached to my electric drill. I ended up preferring this method as it allows for an easier mental visualization of the amount of abrasion. Specifically, I measured my drill to spin, with grinding wheel, ~26 times per second (~1560 rpm) with the wheel having a circumference of 1.56 inches meaning there is an abrasion distance of ~40.56 inches per second (3 feet 4.56 inches). Or in other words, for every second that the grinding wheel runs, it would be equivalent to running the fabric over a 3 foot 4.56 inch grinding stone that has a similar roughness as concrete. 

With the grinder I found that George can handle about 9 seconds of grinding before a hole forms (Figure 4A), which turned out to be the worst of all tested candidate fabrics. Of the other fabrics, rip-stop cotton 10 (Figure 4E) performed the best for the cotton group (Figure 4b-4E) while the Jacquard Hemp 9.9 and the plain hemp 11.5 (Figure 4G-4H) again performed the best out of all candidates (Figure 4A). The hemp fabrics performed well to the point where the projected distance that was needed to wear through Jacquard Hemp 9.9 and the plain hemp 11.5was approximately 121.6 feet (~40 yards), which is four times better when compared to George’s 30.4 feet (~10 yards).

Tear resistance

The final measurement that I took was to see how easy it is to tear the fabric. To make the measurement, I clamped the fabric down leaving some overhanging fabric to be grabbed with vice grip plyers. Then, using the force meter attached to the vice grip plyers, the overhanging fabric is torn from the large piece. What resulted was a grouping of the cotton fabrics towards the bottom in tear resistance where only the rip-stop cotton 10 (Figure 5A, 5E) was able to be significantly more tear resistant than George (P-value 0.0492 T-test). Further, in what seems to be a common theme for today’s tests, each Hemp fabric was significantly more tear resistant than any cotton fabric (Figure 5A) (All P-values less than 0.003, T-test) with plain hemp 11.5 being the most tear resistant followed by Jacquard Hemp 9.9. It should also be noted that the tears that formed in the cotton fibers were cleaner (Figure 5B-5E) as compared to the Hemp fibers (Figure 5F-5H) that are much more frayed at the location of the tear. I interpret this as the tearing in cotton being due to the breaking of the cotton fibers prior to the loss of the structure of the weave, while in hemp there was a loss of the weave structure prior to the breaking of the fibers. If this was the case, I surmise that finishing of the edges with certain stitches to maintain the weave structure would increase the force required for tearing. It should be noted that all candidate fabrics had raw edges.

Discussion

Keeping in mind that this studies’ main goal was to determine which fabric is best for pocket bags, I feel that we got to the bottom of it. Generally, I can say hemp fibers performed much better than cotton. I am actually a little disappointed with the performance of cotton where even the higher quality fabrics did not perform much better than our cheapest cotton fabric (1 square yard purchased for less than $3.00). I would bet that many mass-produced jeans makers already know that and that is why they use the lower cost option without sacrificing too much performance. This does beg the question of whether or not many higher end denim jeans makers know this (I bet they do). It Is also entirely possible that there are some cotton fabrics that do perform better, but we did not test them here today.

Digging down into the reason for why cotton performed worse than hemp most likely lies within the fiber itself. It is known that hemp fibers are stronger than cotton threads, and my results back that up when you look at the puncture and tearing images (Figures 3B-3H and 5B-5H). Specifically, I see that in the puncture and tearing tests that in hemp the structure of the weave was compromised prior to the fibers breaking, while the opposite is true for cotton where the fibers were breaking before the structure was lost. This suggests that the hemp fabrics may have been more tear resistant if the weave structure was maintained. Therefore, I believe this would be an added benefit for the use of hemp fabrics in pocket bags because they will be sewn into the jeans, allowing the maintenance of the weave integrity from all sides. Potentially, this would increase the performance of the fabric overall.  

To determine which hemp fabric would be the best largely comes down to two contenders, and they are the Jacquard Hemp 9.9 and the plain hemp 11.5. That being said, the plain hemp 5.9 did perform well, but I believe its loose weave did hinder its puncture and abrasion resistance making it a less viable option. The performance between the Jacquard Hemp 9.9 and the plain hemp 11.5 was largely similar for the puncture and abrasion tests with the only difference being found in the tear resistance. However, knowing that these fabrics will be sewn into the jeans, they may have a limited shear force so this added tear resistance shouldn’t be the only deciding factor. What may ultimately be the deciding factor may be aesthetics, feel, or feasibility. For example, the plain hemp 11.5 is a thick material that when doubled up for a pocket bag may be too bulky and may override the added tearing strength. This bulk could be an added benefit, or curse, for denim fading if you would like to see the outline of your pocket bags fade into your denim jeans. Alternatively, the Jacquard Hemp 9.9 is a lighter thinner fabric that has a softer feel, and an interesting weave, so these aesthetic features may make it a good choice as well. Altogether, we showed that hemp fibers perform better than cotton when investigating puncture, abrasion, and tear resistance and, of the tested fabrics, the Jacquard Hemp 9.9 and the plain hemp 11.5 are the best candidates for pocket bags for the next chapter of the Iron Snail’s selvedge denim jeans.

This issue of the Proceedings of the Ferrous Mollusk is written by Zachary Wayne.