Sacha Holub

Material Selection

Sacha Holub
Material Selection

Material selection is the obvious stage at which to address sustainability. Whatever materials are chosen have a knock-on effect on the other stages in a shoe's lifecycle. This section aims to highlight the most commonly used materials in the footwear industry and provide information on the negative impact that they have on people and the environment. In contrast, we've listed some better alternatives that try to avoid these problems.

 
 

Common Materials

The following tables list commonly used materials for a shoe's upper, sole, heel and joining methods. These are materials chosen for their low cost combined with their ability for an easy and speedy manufacture. We've described why each material is used, how it's harmful to us and our environment, the size of it's impact and suggestions for better alternatives.

 

   UPPERS

MaterialDescriptionUseEffect on humansEffect on environmentSize of impactBetter Materials

Chrome-Tanned Leather

Chromium is a heavy metal used as a leather tanning agent.Chromium is a cheap, fast method of tanning leather. This leather is more likely to be soft, pliable and stable in water compared to other methods. [1] [2]Tannery workers exposed to Chromium are at risk of damage to gastrointestinal, respiratory and reproductive systems. Chromium is also carcinogenic. [1]Tannery waste contaminates water sources through negligence, e.g. dumping hides onto riverbanks. Contamination can accumulate in food sources e.g. local fish supplies. [2]16 million people are at risk of Chromium exposure globally according to the Blacksmith Institute. [1]
Formaldehye is a chemical compound (CH2O) used in tanning leather.Formaldehyde is used in a number of ways throughout the leather tanning process e.g. as an adhesive or as a tanning agent. The result is pale in colour so hides are referred to as "wet-white".Inhaled formaldehyde (at concentrations above 0.1ppm in air) can potentially result in watery eyes, headache, a burning sensation in the throat, and difficulty breathing. Formaldehyde is also classified as a carcinogen. [3]UnknownFormaldehyde tanning is nowhere near as common as Chrome tanning, but the health effects as a result of exposure in tanneries are known and it's being phased out.
Conventional (Non-Organic) CottonChemicals, referred to as pesticides, are used in cotton production to kill, repel or stop the growth of organisms, by impairing biological processes essential for living. The most commonly used pesticides are insecticides that go by the names of Malathion, Aldicarb and Parathion. [4]Pesticides are used to obtain a higher cotton yield.Pesticides also impact human health, not just the intended pest. The effects from poisoning range from headaches, vomiting and difficulty breathing to impaired memory, disorientation and severe depression. [4]After applying pesticides, rain often washes it away - this happens to 1 million tonnes every year due to excessive application. Major cotton producing countries, like the USA and India, have detected pesticides in their water resources. [4]The EJ Foundation says that "cotton is the world’s most important non-food agricultural commodity" [4], but cotton production means that there are 7 million people at risk to pesticide exposure. [2]
Basic (Cationic) DyesDyeing is a method of applying colour to a textile. This can happen at any stage in the manufacture process; dyes can be applied to fibres, yarn, fabric or a completed article of clothing.Basic dyes dye acrylic fibres.Dyes are made from a variety of chemicals and compounds e.g. sulfuric acid, chromium, copper and other metallic elements. "The World Bank estimates that textile dyeing and treatment contribute up to 17-20% of total industrial water pollution." [5] This pollution can enter the water supplies of local communities and wildlife. "Conventional textile dyeing is extremely water and chemical-intensive: for every two pounds of textiles dyed, 25-40 gallons of water is used." [6]
Acid DyesAcid dyes dye protein fibres (e.g. wool, silk) and nylon.
Disperse DyesDisperse dyes dye polyester yarn.
Vat DyesVat and direct dyes dye cotton yarn.
Direct (Substantive) Dyes
Durable Water Repellent (DWR) treated fabricsThe Greenpeace 'Detox Outdoor' campaign describes PFCs as "a family of man-made, fluorine-containing chemicals".The purpose of using PFCs is to make clothing and accessories waterproof.PFCs can accumulate in the human body - they've been detected in blood and breast milk around the world. [7] "Research has shown that some PFCs cause harm to reproduction, promote the growth of tumors and affect the hormone system.” [8]PFCs are resistant to breakdown and have the potential to remain in the environment for hundreads of years. Research on animals has shown PFCs cause tumors, cancer and reproductive problems. [8]"Several scientific studies have already shown that PFCs can be found around the globe, including in remote areas." [8] “Even if production were to end today, PFC pollution would remain the environment for many years to come.” [7]
PVC (polyvinyl chloride)
See Sole - PVC (polyvinyl chloride)
 

   Soles

MaterialDescriptionUseEffect on humansEffect on environmentSize of impactBetter Materials
Chrome-Tanned LeatherChromium is a heavy metal used as a leather tanning agent. Leather is commonly used as an outsole.
See Upper - Chromium
Vegetable-Tanned Leather

PVC (polyvinyl chloride)

A versatile plastic that accounts for 20% of all plastics manufactured worldwide. [9]In footwear, PVC is often found in outsoles as well as synthetic leathers and coated fabrics for a shoe's upper.Directly (from oil extraction e.g. rashes, chronic headaches, vomiting for those living near oil extraction sites with severe long term effects like lung disease, liver and kidney damage and miscarriages) [10] and indirectly affected (through environmental damage i.e. you eat what your fish supply eats).Crude oil extraction causes problems like deforestation, oil spills, pollution of toxic chemicals. [10] [11] From the 100 million tonnes of plastic produced each year, 10 million tonnes ends up in the sea. Plastic doesn't break down like natural materials - there's an area of floating plastic the size of Turkey in the North Pacific. [12]OOil spills are difficult to clean up and described as impossible, in the case of Artic oil reserves. [1]Bioplastics
PUA rigid type of polyurethane plastic.Used in outsoles because of it's flexibility, resistance to abrasion, strength and durability. [13]
TPU (thermoplastic polyurethane)An elastic, flexible type of polyurethane plastic.Used in outsoles because of it's elasticity, flexbility and resistance to abrasion, impact and weather.
EVA Foam (ethylene vinyl acetate)A tough but flexible plastic.To provide a level of comfort in a shoe's insole.
Petroleum RubberA tough, elastic polymer.Used in outsoles.Rashes, chronic headaches, vomiting for those living near oil extraction sites with severe long term effects of exposure like lung disease, liver and kidney damage and miscarriages. [10]Crude oil extraction causes the problems like deforestation, oil spills, pollution of toxic chemicals. [10] [11]To put synthetic rubber production into context, aproximately 70% of all rubber used is synthetic. [14] When oil spills occurs, they're difficult to clean up and described as impossible in the case of Artic oil reserves. [11]Natural Rubber
Illegally Logged Wood""Illegal logging and related trade occurs when timber is harvested, transported, processed, bought or sold in violation of national or sub-national laws." [15]Used in midsoles for wedges and platforms.Illegal logging aids deforestation, the loss of biodiversity and climate change. "This creates social conflict with indigenous and local populations and leads to violence, crime and human rights abuses." [16]Illegal logging aids deforestation, the loss of biodiversity and climate change. [16]In 2015, illegal imports accounted for nearly 10% of total trade. [17] "It is estimated that some 1.6 billion people worldwide depend on forests for their livelihood and 60 million indigenous peoples depend on forests for their subsistence." [16]FSC-Certified Wood
 

   Heels

MaterialDescriptionUseEffect on humansEffect on environmentSize of impactBetter Materials
ABS (Acrylonitrile Butadiene Styrene)ABS is one of the plastics used to make heels. It's a low cost, easy to machine plastic with good impact resistance, strength and stiffness.ABS is moulded to create high heels and is reinforced with an internal tube of metal.Directly (from oil extraction e.g. rashes, chronic headaches, vomiting for those living near oil extraction sites with severe long term effects like lung disease, liver and kidney damage and miscarriages) [10] and indirectly affected (through environmental damage i.e. you eat what your fish supply eats).Crude oil extraction causes problems like deforestation, oil spills, pollution of toxic chemicals. [10] [11] From the 100 million tonnes of plastic produced each year, 10 million tonnes ends up in the sea. Plastic doesn't break down like natural materials - there's an area of floating plastic the size of Turkey in the North Pacific. [12]Oil spills are difficult to clean up and described as impossible, in the case of Artic oil reserves. [11]
 

   JOINING METHODS

MaterialDescriptionUseEffect on humansEffect on environmentSize of impactBetter Materials
Solvent-Based AdhesivesHazardous chemical subsances used in the manufacturing of adhesives e.g. Benzene and Toulene. [18]Adhesives used in shoe construction, and more often that not, in cheap, poor quality shoe construction.Chinese shoemakers were reported to have high levels of exposures to benzene, toluene and other toxic solvents. [18] The solvents in Benzene are reported to cause harm to the respiratory system and brain, and is classified as a carcinogen.UnknownUnknownWater-based Glue e.g. Renia Aquilim 315 or Irutex™ FI 4006 1K or avoid altogether and purely use stitching methods
 

 

Better Materials

Looking for sustainable footwear materials? Having put together a list of commonly used materials, it's only right for us to suggest some better alternatives for a shoe's upper, sole, heel and joining methods. Most are commercially available and have already been put to good use by other brands, whilst others are still in development and offer promising solutions.

 

   UPPERS

Alternative forMaterialDescriptionAvailabilitySustainable qualitiesOther benefitsDisadvantagesExamples of use

Leather

BiocoutureA bacterial cellulose fabric, grown from fermented tea, bacteria, yeast and other microorganisms.In developmentThis leather alternative is a non-animal-based material that could be made from waste streams e.g. food processing plant. It's also biodegradable.Clothing and accessories can be formed conventionally through sewing, or when wet, it can be formed around a 3D shape.Not yet water-resistant and has not yet been industrially scaled.Liz Ciokajlo
Cellulosic Fiber

Cork Sheeting

Cork is the bark of the cork oak tree.Commercially available"It is a 100% natural raw material, that is 100% reusable and 100% recyclable, extracted from cork oaks without harming the normal development of the species and without damaging the tree." [19]Cork is a soft, lightweight, compressible and hypoallergenic material.It can be scratched or dented when under pressure.
Eco-Leather"Flax or cotton and plant oils are laminated together in layers to create a breathable, leather-like material." [20]In developmentA plant-based alternative made by mixing flax or cotton fibers with plant oils. This is laminated togeather to create a material that feels and acts like animal leather.BreathableStill in development and working out problems like stiffness.
Modern MeadowAnimal-free leather grown from living cells: "Modern Meadow biofabricates leather from collagen protein and other essential building blocks found in animal skin, without involving animals." [44]In developmentModern Meadow is reimagining the age old-traditions of the leather industry in a way that doens't harm animals and the environment - their "biofabricated leather also reduces waste by up to 80% compared to traditional leather" [44]"Biofabrication re-creates aspects of traditional leather, including suppleness and breathability, while enabling new properties not possible from animal hide, such as improved strength to weight ratio." [44]Modern Meadow's material is still in development.Unknown

MuSkin

A vegetable alternative to leather that is " a skin extracted from the mushroom hat and is processed in a manner totally similar to that animal, with a tanning, however, entirely natural." [40]Commercially availableMuSkin has the appearance of suede and "The total absence of chemicals makes Muskin totally non-toxic and therefore ideal for use in the manufacture of items that are in direct contact with the skin." [40]"From laboratory tests it has been shown that this new skin, delivers great performance. In fact, in addition to not promote the proliferation of bacteria, has a strong capacity to absorb moisture and then releases it." This makes it ideal for shoe insoles."The production capacity is, at this moment, of 40-50 sq.meters/month." [41] Also, the appearence and thickness of MuSkin is also uneven, which may rule it out for applications where high quality, grade A leather is used.Unknown

Mycelium

A leather substitute engineered by MycoWorks that is grown from mycelium and agricultural byproducts.In developmentMycoWorks' material is manufactured in a closed-loop process using "abundant, natural fibers to create 100% biodegradable materials, making this an infinitely renewable technology". [43] The material is also animal-free.The MycoWorks material can compete with conventional leathers due to it's strength, flexibility and durability. This is a cost competitive leather substitute because it "takes a fraction of the time and resources to grow" [43] in comparison to making leather from raw hidesMycoWorks is still collecting information on fungi products.Unknown
Piñatex™A non-woven textile made from pineapple leaf fibres.Commercially available“Piñatex fibres are the by-product of the pineapple harvest. No extra land, water, fertilizers or pesticides are required to produce them.” [21]Piñatex™ is a strong, breathable, soft, light and flexible textile. Various thicknesses and finishes are available, and the extraction of pineapple leaf fibres creates additional revenue for the farmers.Unknown
Chrome-tanned leather (a.k.a. wet blue)Vegetable-tanned leatherVegetable tanning uses tannins that occur naturally in the leaves and bark of certain plants.Commercially availableAvoids the use of toxic chemicals like Chrome, instead using naturally occuring tannins.UnknownVegetable-tanned leather isn't as soft and pliable as Chome-tanned leather. Vegetable tanning is also a more time-intensive process.
Rhubarb leather®A form of vegetable tanning but using tannins extracted from rhubarb roots.Commercially availableAvoids the use of toxic chemicals like Chromium, instead using naturally occuring tannins. Also, Rhubarb leather® is fully produced in Germany. "Even the rawhides come from regional resources with short transport distances" [22]Rhubarb leather® is suitable for allergy sufferers because no chromium salts or heavy metals are used.Whilst it offers a safer alternative to traditional Chromium tanning, it is still a method of tanning leather - a material that is ethically challenging.Deepmello
wet-green®An environmentally friendly tanning agent to provide an alternative, sustainable method of tanning leather. wet-green® is an example of biomimicry, using the same substance that the leaves if the olive tree uses to ward of predators.Commercially availableCompletely harmless across the entire value chain through eliminatinating the use of substances like acids or salts. Also, "No tree is felled, no plant sacrificed and no fields cultivated which would otherwise be used to produce food". [23]It produces a similar quality to Chrome-tanned Leather with a softness, lightness and durability. wet-green® also has a pleasant fragrance in contrast to foul smell of Chrome-Tanned Leather. [23]Whilst it offers a safer alternative to traditional Chrome of Formaldehyde tanning, it is still a method of tanning leather - a material that is largely, not ethical.BMW

Suede/ Nubuck

Ultrasuede®A man-made suede / nubuck alternative, derived from recycled polyester.Commercially availableThese microfibres are manufactured from recycled polyester. "Recycling polyester means reducing energy consumption and CO2 emissions into the atmosphere by 80% compared to the traditional petrol-based polyester production process." [24]Ultrasuede® is machine washable and resistant to stains and discolouration.Unknown
Dinamica®An eco-suede made from recycled polyester.Commercially available"Recycling polyester means reducing energy consumption and CO2 emissions into the atmosphere by 80% compared to the traditional petrol-based polyester production process." [24] "Dinamica® is designed for easy disposal, and is 100% recyclable at the end of its useful life." [24]UnknownUnknownBeyond Skin

Non-organic Cotton

Bast FibresBast fibres are a group of natural fibres that are extracted from the stem of certain plants e.g. flax (linen), hemp, jute and stinging nettles.Commercially availableBast fibres can be grown with fewer imputs, like without pesticides and smaller areas of land. They can also be grown in European climates, providing alternatives as oil prices and transportation costs rise.Bast fibres are durable and flame retardant.However, bast fibres are not as soft as cotton.
Polyester-Based FabricsBiosteelAn artificial silk fibre created using the same proteins that spiders use to make their silk.Commercially available100% biodegradable once placed in water with the digestion enzyme called proteinase within 36 hours. [42]Biosteel is 15% lighter [42] than traditional polymer shoes and offers controlled moisture management - ideal for atheletes. The fibre is also non-allergenic, vegan.UnknownAdidas
ClimatexA biodegradable fabric primarily used to upholster office furniture.Commercially available100% biodegradable, "safe enough to eat" [25], scraps are sold on to farmers as mulch, improved the local water supply, high quality water treatment.Climatex is a forward thinker - sharing the recipe for their fabric free of charge. "It’s not really green thinking if we just hold that information secret." Bonnie Sonnenschein [25]UnknownPo-Zu
Thread InternationalA range of recycled PET fabric.Commercially availableMade from "100% post-consumer recycled content responsibly sourced from Haiti or Honduras" [26]. Thread International provides "Ground to Good™ traceability at all levels of the supply chain from bottle collection to fabric production." [26]A variety of options are available e.g. jersey, canvas and denim.UnknownTimberland

Conventional Dyes

Low-Impact Reactive DyesReactive dyes are a class of coloured organic substances that tint fabrics through chemical bonding between the fibre and molecule of the dye. [27]Commercially available"Generally, low impact dyes do not contain toxic chemicals or mordants (which fix the dye to the fabric), require less rinsing and have a high absorption rate in the fabric (~70%). High absorption rates and a decreased use of rinse water create less waste water." [28]"Reactive dyes were originally used for cellulose fibers only but now their various types are used for wool, silk, nylon, acrylics and their blends as well." [29]Reactive dyes are made from synthetic petrochemicals like environmentally damaging dyes, the method requires a high concentration of salt, and it's an expensive process in comparison to conventional dye methods. [28]Unknown
DyeCooDyeCoo is a method of dyeing fabric that uses "uses reclaimed CO₂ as the dyeing medium in a closed loop process" instead of water. [30]Commercially available"No process chemicals, no water, no waste water and therefore no waste water treatment is necessary." [30]"Short batch cycles, efficient dye use, no waste water treatment all contribute to significantly reduced operating costs." [30]DyeCoo's technology can only be applied to polyester fabrics.Nike

PFC-free membranes

SympatexA PFC-free membrane that "absorbs the water vapour and removes it through the clothing to the outside. This keeps the body warm and dry even in extreme situations.” [31]Commercially availableIt contains no PTFE (Polytetra-fluoroethylene) whose manufacture, disposal and incineration can release harmful substances. Sympatex can also be recycled using existing methods, e.g. PET bottles.Sympatex is machine washable, wind proof and has elastic properties.UnknownVaude
PFC finishes

Bionic-Finish®EcoA water, oil and soil repellent finish for textiles.Commercially available“No perfluorinated compounds are used for manufacturing BIONIC-FINISH® ECO products." [32]There is no impact on breathability.Unknown
  • H&M
  • Po-Zu
  • NikwaxA water-based wax finish that waterproofs products.Commercially availableNikwax is a non-toxic way to waterproof gear without the use of fluorocarbons or propellant gases. It's also not animal tested.Machine washableAn extra step of prewashing (using a Nikwax product) is recommended, which removes any existing dirt. Reapplication is suggested, every 4-6 washes or once a year.
     

       Soles

    Alternative forMaterialDescriptionAvailabilitySustainable qualitiesOther benefitsDisadvantagesExamples of use

    Synthetic Rubber

    Natural Rubber e.g. LACTAE HEVEA®A natural rubber material made from the milk of the Hevea tree. The Hevea tree "is only one of at least 2,500 plant species that can produce this high performance polymer". [33]Commercially availableThe harvesting of the hevea milk helps the tree to flourish rather than weakening it. "No natural forest is cut down. After 25 years of exploitation, the old tree is felled and a new tree is planted." [34]The pockets of air in the microstructure provide excellent comfort and shock absorbance.Over time, "Slight visual imperfections resulting from the natural origin of the sole" often refered to as 'bloom' appear - these are viewed as proof of authenticity [34] and can be removed with an oil.

    PU or EVA Foam

    CoirA short, coarse fibre extracted from coconut husks. It's often combined with natural rubber for cushioning applications e.g. mattresses or a shoe midsole.Commercially availableCoir is a natural material, so will biodegrade.Coir is an example of biomimicry; a natural shock absorber for coconuts which can be utilised for comfort. Coir also provides good resistance to bacteria.UnknownPo-Zu
    Cork Sheeting

    See Uppers - Cork Sheeting

    Petroleum-Based Plastics

    BioplasticsAccording to European Bioplastics, if a plastic material is either biobased or biodegradable, it can be called a bioplastic. [35]Commercially availableSome bioplastics are made from natural, renewable materials, some biodegrade after use and some can do both. "Some biopolymers, such as PLAs and PHAs, have shown early promise as more sustainable alternatives." [36]Some bioplastics mimic tradition petroleum-based plastics in their appearence and performance.TThere's a lot of variation within the bioplastic family: "Some have trouble standing up to even moderately high temperatures. Some become brittle at even moderately low temperatures. Some are simply too expensive to be manufactured as plastics on a large scale." [36]One Moment

    TPU

    EcoTPUA bioplastic alternative for TPU.Commercially availableEcoTPU is made with 60% of the material from renewable plant origins.EcoTPU holds the same properties as oil derived TPU.UnknownNike
     

       Heels

    Alternative forMaterialDescriptionAvailabilitySustainable qualitiesOther benefitsDisadvantagesExamples of use

    Illegally Logged Wood

    FSC-Certified WoodFSC (Forest Stewardship Council) "is an international, non-governmental organisation dedicated to promoting responsible management of the world‘s forests." [37] They have developed a certification for responsibily sourced wood, paper etc.Commercially availableFSC certified operations increase the size and number of protected forest areas, retain wildlife habitats and retain carbon longer. [38]FSC certification has social and economic benefits like helping to resolve conflict with local communities and preventing unauthorised activities e.g. harvesting. [42]It's possible for companies holding FSC certification to potentially trade in illegal products. "A company can hold FSC certificates, but that does not mean that all of its products are necessarily FSC certified." [39]
    Petroleum-Based PlasticsBioplastics
    See Sole - Bioplastics
     

       JOINING METHODS

    Alternative forMaterialDescriptionAvailabilitySustainable qualitiesOther benefitsDisadvantagesExamples of use

    Solvent-based glues

    Renia Aquilim 315A water-based glue.Commercially availableFree from solvents.UnknownRenia Aquilim 315 is water resistant, but it's best used for applications where it won't constantly be exposed to water.Lisa Sorrell
    Irutex™ FI 4006 1KPo-Zu
     

    Looking to continue your materials research? Try the following:


    References