Cowhide

Tanned animal hides, once an essential part of our ancestors’ survival, have become a luxury material used in fashion, transportation, tools and upholstery. It is breathable, tough and ranges from coarse and stiff to very soft and flexible. Around half of all cowhide goes into the production of footwear (shoes and boots). The rest is used in garments, luggage, stationery (book binding), upholstery, automotive and transportation applications.

Many types have evolved, and cowhide exists in all formats, from hair-on hide through high-gloss plastic coated patent leather. Hides are valuable and not solely a by-product of the meat and dairy industry. There are concerns about animal welfare, water consumption (c. 350 litres per 1 m2 of leather) and antibiotic use. While schemes exist to protect animals, leather sales contribute in part to the mass production of animals for meat and materials, which has its own ethical issues.

The carbon footprint presented here only takes data from after the slaughterhouse – 10-20 kg CO2/kg is already a significant number if you compare it to synthetic fibres. If it were to include rearing the cattle, then it would be in the region of 120 kg CO2/kg.

Many synthetic leather alternatives to genuine leather exist, sometimes marketed as vegan leather but also referred to as leatherette, imitation leather, faux leather, manmade leather and pleather. The most common are based on polyurethane resin (PUR) or polyvinyl chloride (PVC) coated textile. They are referred to as PU-leather and PVC-leather. The highest quality are based on nonwovens microfibres, such as thermoplastic polyurethane (TPU), which mimic the fibrous structure of genuine leather. They are utilised in footwear, linings, bags and sports goods, for example.

Natural alternatives to animal leather include fungi (mycelium and Phellinus) and leaf fibre textiles. For example, Piñatex is a nonwoven textile made up of piña fibre (from pineapple leaves), coated with polylactic acid (PLA) produced from corn starch.

Leather quality and surface grain is determined in part by the animal – calf, cow and buffalo – with younger animals yielding more supple leather. Appearance is governed by the choice of process, including tanning, dyeing and finishing. Tanning is fundamental for the preservation of the skin. It is a curing process, whereby fats and non fibrous proteins are removed, and the bonds between the collagen (fibrous protein) are strengthened. This makes the leather durable, water-resistant and non-perishable. Tanning agents are derived from mineral salts (such as chromium sulphate), synthetic (such as phenol and naphthalene) or vegetable sources (tannin).

Chrome tanning (using trivalent chromium) is the most popular. It is relatively fast, taking only 20 hours, and yields consistent results. It turns the leather blue (semi finished chrome tanned leather is known as wet blue), and so requires dyeing to correct the colour. There are several principal types:
– Full grain aniline leather is the highest quality chrome tanned leather with the surface of the skin intact, blemishes and all. It is dyed, but left uncoated to retain the natural quality and feel. Therefore, only the highest quality leather tends to be finished in this way. Uses include footwear, bags, jackets, upholstery and other premium items.
– Semi-aniline has been pigmented and coated to provide some resistance to wear and staining. It is used in application that will likely have a lot of wear and tear, such as upholstery and luggage. For example, taurillon calfskin, a very high quality semi-aniline leather used in some of the most expensive bags, wallets and purses.
– Nubuck leather is buffed on the top side to produce a roughened, more hard-wearing surface, as is typical on workbooks and can be found in bags, gloves and outerwear.
– Suede is produced from split leather, which is napped (abraded with emery sandpaper) to pull up the fibres. The appearance can vary, but it will not be as fine or tough as nubuck owing to the looser fibre structure. It is applied in linings, for comfort and away from rain and dirt, such as in footwear and bags.
– Pigmented leather is coated with plastic, making it even more resistant to wearing, staining and fading. It is also known as epi leather and used in jackets, bags, upholstery and car interiors, for example.
– Patent leather has a heavy plastic coating, to create the super high gloss finish. The surface appears striking when new, because gloss enhances colour saturation, but will fade as it becomes scratched and scuffed. To be classified as patent, the plastic coating – typically polyurethane resin (PUR) or polyvinyl chloride (PVC) – must be no more than 0.15 mm. If the coating is greater than this, but less than half the total thickness of the finished material, it is classified as patent laminated leather. This finish can be combined with embossing to create leather effect.

Light coloured and white leather is produced using a mix of mineral salts and synthetic tanning agents. Also known as wet white, it has a pleasant handle and good softness, but is a little more expensive. Being chrome-free, it is preferred by the automotive industry and for certain types of clothing (such as babies’ clothes), and is safe to compost and incinerate.

Vegetable tanning uses bark, seeds and leaves. It is an age-old process, that can take up to a year, and yields a naturally coloured leather, which tends to be stronger and more hard-wearing than chrome-tanned leather. The surface patina will develop more quickly than with other types, and it is not as long lasting. Vachetta leather, for example, is left untreated to encourage a natural patina to develop. As with wet white leather, it may be composted or incinerated end of life.

The location of the leather on the animal will affect its properties, such as thickness, suppleness, elasticity and strength:
– The bend (butt) produces the strongest and thickest leather. It is used in saddles, belts, safety hats (such as the American firefighting helmet), shoes and boots.
– The culatta is the rear part of the skin, made up of the belly middles and hind shanks. It is used in belts, shoes and handbags, for example. The properties of the belly and shank are different, and items made of this leather can take advantage of that.
– The belly produces thick and not very strong leather. It is pliable and can be moulded. It is not considered high quality and typically used for shoe linings.

Leather is sold in mm, or oz. The scale is based on increments of 0.2 mm, or 0.5 oz. For comparison, calfskin is typically 0.6-1.2 mm, and 1.5-3 oz; and steer hide is around 2-5.6 mm, and 5-14 oz. Upholstery uses 2.5–3 oz; footwear uppers are typically constructed from 5–5.5 oz (soles are heavier and around 12–14 oz); bags, purses and small cases use up to 6–7 oz; and belts and holsters are produced from 8–10 oz.