There can be upwards of 70 materials and components that go into making shoes versus five for a t-shirt. Even basic kid's shoes, an example of what a breakout of materials could look like below, require a multitude of materials.
While apparel is made predominantly from textiles, shoes contain an exorbitant number of diverse materials and components – increasingly made up of more plant based and recycled content – including:
Stainless Steel Wire
White Glue (PVA)
A brand may manufacture 30 different types of shoes, per season, each with different materials from multiple suppliers based in different countries – resulting in huge traceability challenges and complexities not really seen in apparel.
T-shirts need a sewing machine and a few hands. Traditional shoe manufacturing requires large machines and assembly lines where there are over 100 touches for each pair of shoes.
Shoe factories often employee hundreds of people manufacturing shoes because of the complexity of cutting, sewing, attaching multiple layered materials (backings and reinforcements), finishing and artisan needs.
“…materials can be cut and sewn conventionally, but can also be laser cut, RF welded, hot pressed, cold pressed, co-molded, perforated, and over-molded; all on one shoe!” (Wade and Andrea Motawi, Shoe Material Design Guide. P. 32, 2017)
Unlike apparel, many materials must be bonded together to provide toughness, body, and durability for consumer use; common examples are fabric backing (adding liquid resin and or coatings) and lamination. This adds additional processes and complexity in production but also requires unique disassembly techniques not found in most apparel items. Footwear companies are working to add more recycled or bio-based materials to displace traditional materials here, but performance will continue to require the above complex assembly.
Affixing the upper to the outsole midsole on nearly all sneakers, for example, also requires glue in 12 areas across a shoe, adding to the complex process and requiring a great focus on details. This does not even account for the work needed to attach metal hardware like eyelets or inserting metal shanks for boots or heels.
Shoes must perform to higher regulatory standards than most other products because they are under constant pressure by consumers in constant motion. Imagine firefighters, nurses or construction workers. Shoes must be manufactured with multiple performance factors not found in apparel including:
slip resistance (see picture of test machine)
flexibility (see bottom picture of test machine)
durability and weight support
All of this is needed for the full safety of the consumer to protect against slipping, twisted ankles, and other health related issues.
Inside a shoe are hidden materials and components needed to ensure performance, vastly different than apparel functions. Some of these include:
toe and heel counters
toe rand reinforcements
eye stay reinforcements
A multitude of materials, many affixed together, make it hard to recycle footwear. Some companies have programs to recycle their shoes, others are designing for disassembly. However, there is no such infrastructure to recycle large amounts of dissimilar footwear across the industry.
Added to this is the fact there are a multitude of construction types needed to understand how to effectively separate the upper from the bottom to have a better chance of isolating materials for increased recyclability. Including:
Goodyear welt construction
Norwegian storm welt construction
Stich down Veldtschoen welt construction
List and Photo Source: (How Shoes Are Made. 2018. P. 27–28)
Shoes require more than a machine to grind unusable shoes. You need a team of experts who understand the materials across the shoe as well as how it is constructed to disassemble footwear. This may require sorting shoes into construction categories and specific machines. Thus, a much different circular infrastructure and model is required than apparel, one that is not reflected in most suggested policies.
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