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    Why are we using a Synthetic Outsole for Our Boots?

    Hey folks,

    I'm back with another educational newsletter about our ongoing quest to make you the perfect pair of boots! I know my inbox has been blowing up with nonstop holiday ads from the select companies I follow, so I hope this is a welcome break for you too =)


    If you missed the last newsletter, here's a link to a web version. If you read it, here's a one-paragraph recap: 

    One of my style-savvy customers told me to make a boot for our next product. I researched all the various boot styles, and decided that a 6-inch open-lace boot covered the most ground alongside our oxfords. We made our first sample using Cement Construction and our hollow-heel outsole, just like our oxfords. I immediately liked them more than our oxfords because of the versatility and performance. In Dec 2013, Vivobarefoot released their Porto, and I got a chance to see that an outsole that is clearly flat doesn't look too bad, because we've seen similar in wedge sole boots. So, we looked into Goodyear Welt construction, which offered many advantages (use of oily rich leathers, solid outsole attachment, easier resoles and more of them), as well as disadvantages (less flexible, less groundfeel, more expensive, loss of a dressy heel). In the end, I decided to develop our first boots as a Goodyear welt because I feel it makes the best boots for you.

    Now, let's continue the story!

    Prototype 2: Black Trek Leather Upper, Goodyear Welt Construction, Leather Outsole

    Since the GYW is a traditional construction method, I decided to pair it with the most traditional type of outsole: leather.

    Scenic stop in Utah, on my way home from the factory

    The first thing I said when they handed this pair to me at the factory was, "These look fucking cool!" Linda, the product development engineer at Weinbrenner, was quite happy with my response.

    The Break-In Period

    But looks can sometimes kill, right? I've tried on Goodyear Welted leather-soled shoes before, but just for a few steps indoors. This boot was my first time navigating the world in a pair of GYW and leather.  I kept a journal of my thoughts during the break-in process. I can say straight-up that they were uncomfortable to walk in during the first 5 days.

    I asked my friend Ivan, who loves his Red Wing Iron Rangers, if he experienced a break-in period:

    " Yes. It's long, too. I actually don't think mine are fully broke in yet. They typically take 3-6 months to break in, depending on how much you wear them. They hurt like a bitch when they were new, but they're comfy now. "

    Fortunately, it didn't take months. By the 8th day, after about a mile a day of combined walking and running, they were comfortable.

    Slippery Leather Soles

    The stiffness went away and the boots met my standards for flexibility , but another issue never got to an acceptable level for me: slipperiness. 

    I read somewhere that once you start wearing a leather sole shoe outside, all the scuffing would created a textured surface, and it wouldn’t be as slippery anymore. There was an improvement over time, especially compared to how slippery it was brand-new, sure. But I would still experience slips here and there, on hardwood floors and metal stairs, just to name a few. 

    There are some folks who argue that before synthetic soles were prevalent, leather soles were fine for traction, often citing that leather soles had taken climbers to the top of Mt. Everest. To me, this is kind of like saying that biting a bullet is a viable form of anesthetic. It works... but is far inferior to what modern technology has to offer.

    Water & Leather Soles: a Bad Combo

    The slips I experienced were all on dry surfaces. With Prototype 2, I religiously avoided wet conditions. I had been warned from multiple sources how hazardous water was to leather soles. 

    #1, there is the slippage, which we already covered.

    #2, wet leather soles become very prone to physical damage. 

    #3, if water penetrates deep enough and you aren’t able to properly dry them out, that could be the end of your leather soles. Water damaged leather soles become stiff, brittle, and can crack. Even if they were properly dried, salt and chemical residue dissolved in water could remain in the leather and ruin the sole too. 

    Other Drawbacks of Leather Soles

    Water issues aside, here are some more drawbacks to leather soles. 

    #4, leather soles are heavy. Significantly heavier than synthetic.

    #5, leather soles start off quite stiff and inflexible. They are made this way to be durable, but it ain’t comfy. 

    #6, leather soles have much less cushioning and therefore much less groundfeel than an equivalently thick synthetic sole. Leather is a fibrous structure that is good for providing strength, even as it’s being stretched. It makes sense, as that’s what it needs to do in its original form, as skin for the cow! However, the cellular structure of synthetics are made to compress, and it serves our underfoot needs better than leather. 

    I want to note that #4, 5, and 6 are specific to the stiffer vegetable-tanned leather that is traditionally used for soling. BirthdayShoes recently reviewed a pair of SoftStarShoes with Bullhide Soles and the author praised how much flexibility and groundfeel it afforded. Their leather sole appears to be more similar to upper leather than soling leather, so it makes sense. Still, it suffers from the same issues with water, and I can’t imagine soft upper leather lasting very long when you’re walking on it.

    Leather Soles do Look Nicer

    The only redeeming quality of leather soles is that they look nicer. It’s hard to argue against this. A leather sole is able to display much more vivid colors than any synthetic can. And it’s not just the colors, but the texture too. There is an elegance to the natural fibers that can be seen running horizontally. Maybe someday they’ll be able to reproduce the vivid color and natural texture of a leather sole with a synthetic, but right now they can’t. 

    As you can see though, it’s almost no contest! I’m not going to sacrifice all of the functional benefits of a synthetic sole just for a sliver of good looks at the very bottom of my boots.

    Boots in particular are supposed to take on a wider range of weather and terrain conditions than dress shoes. A boot that can't be worn in wet conditions is like an Asian who can't do calculus (oh wait, that's me...).

    For folks like us who prize both style AND utility, the clear winner is the synthetic sole.

    Winner: Synthetic Soles.

    Prototype 3: Cognac Trek Leather Upper, Goodyear Welt Construction, Synthetic Outsole

     Hello, Chicago.

    I was going to keep a break-in journal with Prototype 3 like I did with Prototype 2. But Prototype 3 broke in so quickly (within a day) that there was no need. This pair, compared to Prototype 2, confirmed everything I had learned about leather versus synthetic soles.
    While in Chicago, I stepped into a huge puddle of rain with these, and emerged with my socks and feet completely dry. (The photo above was taken the day after. My, what a beautiful summer day!) There were a couple factors at play here. First, I had properly conditioned my shoes, paying extra attention to the seams. Second, these boots have a gusseted tongue that can deal with a higher waterline than if it was a free floating tongue. Third, in Goodyear Welt construction, there are no stitches running from under the shoe to the inside of the shoe (as opposed to Blake construction). And fourth, the synthetic sole is water proof.

    Now, I’m not saying you should wear your future pair of PriPro boots as puddle-splashers. But if you had to brave a puddle, you could. As you should be able to in a good pair of boots, right? =)

    To Be Continued...

    We've been able to nail down what construction method we want (Goodyear Welt) as well as what outsole type we want (synthetic). However, we still have a number of questions to be answered.

    First, even though we know we want synthetic, what kind of tread pattern do we want, and how thick? 

    Second, what type of upper leather do we want? Boots can be made in a number of different leathers, including pigmented, pullup, and roughout. The subject of leather has been a very interesting (if somewhat frustrating) one, as there are so many to choose from, and a lot of incomplete or inaccurate information based on hearsay.


    Something Useful from my Personal Blog

    Finally, I wanted to share with you an article I wrote on my personal blog: Open Letter from Your Friend with Dietary Restrictions. I know that most of our newsletter subscribers watch what they eat to some extent. If this communicates your own sentiments, effectively and respectfully, please feel free to share.

    Thanks for tuning in, and happy holidays! Until next time...


    Best Regards,

    Mountain Evan Chang

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