“Using Oil-based Leather Care Products”

Research

Information regarding the care of leather is scarce, often contradictory, misleading, or simply wrong. Misinformation can lead to inadvertent damage to your vehicles leather upholstery; my goal is to present clear, concise, accurate information. 

There is a great deal of conflicting information on leather care being put out by leather experts themselves who use baffling pseudo scientific techno speak as another marketing ploy, which makes it difficult to find a definitive, unbiased answer. It had always confounded me that such a simple subject has been made into something so complicated.

After various meetings and discussions with leather tanners, their chemists and fat liquoring formulators and many leather care product manufacturers I’ve gained an understanding of this versatile material on both a practical and scientific level.

I have always thought that the more facts and information you have at hand the easier it is to judge what information you are being given. After all, how can you fully understand and properly use any product unless you have all the facts? In the final analysis; it’s your vehicle, your hard earned money and your choice

Here is one definitive truth –you are dealing with the leathers finish, not the hide itself.

Materials Technology

Automotive OEM technology is becoming more and more complex requiring educated and skilled technicians to work on them. As the materials used are constantly changing we must maintain our knowledge base and utilize the correct products and application methodologies to keep up with emerging technologies.

Automobile model ranges use different materials for their vehicles interiors; leather upholstery like Aniline Immersion Dyed, Aniline Micro Pigmented, (Urethane) Finished, Artificial leather such as MB-Tex and unfinished materials like Synthetics and Alcantara, and sometimes combinations of products (Alcantara seat inserts on leather seating) as well as various grades of leather hide, full-grain, top-grain and split –grain (which is protected with urethane) all of which require different products and applications methods

Leather Tanning Process

All cowhides are naturally oily, unfortunately, these natural oils are stripped away in the tanning process, which is the process that renders the hide invulnerable to decay and some equivalent oils must be re-introduced after tanning. This last tanning step, the replacement of oils, is called "fat liquoring." Over the centuries, a number of oils have been found that have a natural affinity for leather fibres.

Every leather tanner has his own, unique, blend of tanning oils. These formulas are closely held secrets, passed down through generations; they are neither volatile nor migratory, this is the origin of the new car ‘leather smell’. This is one reason why one company's leather can have a totally different feel, fragrance, texture and softness from another company's product (See article “Fat Liquoring”)

Using Oil-based Leather Care Products

I get more questions on auto leather care than almost any other subject (glass cleaning comes a very close second) 

When it comes to vehicle leather upholstery care information, there are plenty of myths and very few real facts. I hope this extract will provide you with enough commercially unbiased, factual and relevant information to eradicate those myths to enable you to give your car's leather interior the proper care it needs to stay supple and looking great for many years.

Many of the following statements are controversial and are polar opposite of popular leather care practices. I've found that some leather care myths are deliberately perpetuated by the industry, especially those on the use of oil-based leather conditioners and others are just common errors of judgment.

The interior environment of an automobile can be extremely demanding on any material used. Temperatures range from hot dry summer days, to freezing nights. Both high and low humidity, even air conditioning that cools, but also dries. Leather's greatest enemies are; sun, heat, body oils, perspiration (that contains urea as well as organic salts and acids) and ultra violet radiation (UV), which dries the hide, fades the colour by bleaching, and can cause the leather to fail by drying out the fibres causing the urethane and / or the hide to crack.

When leather tanners talk about conditioning leather they are referring to re-hydration; not the replenishment or replacement of the fat liquoring oils and waxes. Modern finished leather needs to be kept hydrated with moisture to ensure the leather remains flexible and maintains its soft tactile feel.

This is done by regularly wiping the surface with a damp 100% cotton micro fibre towel and by using aqueous (water- based) leather care products. There is no reason to use oil-based leather care products to condition or feed leather hides

Automotive leather upholstery is a multi-strata urethane coating that allows hydration (transpiration and evaporation of moisture); consisting of the actual hide, colour pigmentation and the surface finish. An acrylic and polyurethane resin binder system is used to improve flexibility, fastness and adhesion to the leather, then two or three aqueous (water- based) pigmented base coat applications a clear aqueous (water- based) top coat is then applied as the final stage of the finishing process.  

Urethane and pigmented finished leather has micro-pores that allow evaporation and hydration (the passage of water vapour) they are not sealed per se as liquid vapours penetrate it easily; others liquids stay on top dependent upon their molecule size.

The urethane  used for protecting automobile upholstery is classified as a semi-solid permeable membrane, being a thermosetting polymer (elastomers) it remains flexible while retaining its tensile strength, to enable it to expand and contract, following the temperature fluctuations (elasticity) of the substrate.

The urethane although very resilient to abrasion wear from entering and exiting the vehicle, still maintains its physical properties like flexibility, tactile hand and its patina. A urethanes fibre structure will stretch in all directions with no particular grain or stress pattern. The urethane surface coating will  not withstand multi directional stress,  however, and when it’s flexed or stretched continuously in the same place the surface coating develops minute cracks. It also has micro-pores that allow evaporation and hydration (the passage of water vapour through a membrane or pore) they are not sealed per se as some liquids penetrate it easily; others stay on top dependent upon their molecule size

Modern automotive leather upholstery use a completely different tanning  processes and finishing system, utilizing advanced polymers and chemicals (urethane doesn’t require conditioning or rejuvenation) and as a consequence  they do not need to be treated with aftercare products containing oils or proteins.

Oil combines with little bits of dust and dirt, acting like a fine sand paper that wears down the protective coating on your seats as passengers get in and out of your car.  That protective layer makes your leather seats more resilient to scratches, water and heat damage as well as other types of wear and tear, so, once that layer is worn thin, your seats are more susceptible to all types of damage.

The percentage of oil on the weight of leather is quite small, from 3-10 %. The precise manner in which this small quantity of oil is distributed throughout the leather materially affects the subsequent finishing operations and the character of the leather.

Oils and soft plastics i.e. polymers, acrylics and urethanes are not compatible; repeated application on to finished leather can cause the breakdown of cross-linking and binding agents. 

Oil accelerates the deterioration of urethane over time. After extended use the condition of the finished leathers pigmentation (colour) will be removed by the oil causing the urethane protection to become delaminated.

Leather's greatest enemies are; sun, heat, body oils, perspiration (that contains urea as well as organic salts and acids) and ultra violet radiation (UVR), which dries the hide, fades the colour by bleaching, and can cause the leather to fail by drying out the fibres (dehydration) causing them to shrink as well as the nd the  urethane and / or the hide to crack.  Since body dirt and oil are a big stain factor in leather, be cognizant of bare skin when you are in your vehicle. If you use suntan oil or spray tan lotion, be sure to use a towel when you get back in your vehicle so that the oil does not get onto your leather. You can also use a towel when leaving the gym as body oils/ perspiration contain organic acids that will stain.  

Neat’s-foot, Lanolin (Latin: lāna "wool", and oleum, "oil"), Sperm whale oil, Mink Oil  is a euphemistic name for liquefied pig fat and silicone oil, Tea Tree Oil,  even the so-called Banana Oil, btw it is impossible to get any oil derived from a banana, its real name; Isoamyl acetate is a chemical solvent, often used as a ‘cover-up’ aroma. Silicone and oil- based conditioners are all damaging to urethane coated leather, as they block the movement of moisture back and forth (evaporation and hydration) regardless of what they say on the products label.

Beeswax (or any other organic or inorganic wax) and silicone are hydrophobic, which means they will not allow the replacement of moisture lost through evaporation, nor allow the movement of moisture back and forth.

Silicone again, not ideal for leather in the same way wax or oils aren’t, as they seal the surface and make it slippery, something I personally don’t enjoy in any car. I have seen silicone penetration up close and the only way to remove it from within the hide is to chemically break it down as its function is to impregnate itself into the finish and then form a ‘hard’ shell to protect it.

Silicone oils and waxes also helps attract dust, making  it artificially shiny (losing that OEM matte look)  and can help bring on cracks in polyurethane coated surfaces as it builds up with each coat applied. The net effect of which is dehydration leads to drying and cracking of the surface

Silicon oil formulations are build-up type products which accelerate heat damage, oil formulations are greasy and oily, and have a high electrostatic attraction to dust, grime, which will soil more quickly. We absolutely do not recommend these products for any type of leather application. I have seen silicone penetration up close and the only way to remove it from within the hide is to chemically break it down as its function is to impregnate itself into the finish to harden and "protect" it.

When applied to leather they don’t facilitate the leather or covered lather to receive any hydration, causing it to dry out; it may also have a detrimental effect on the urethane by causing fissure (cracks). Once it permeates the foam and / or hide to remove requires the use of chemicals to break it down as its function is to solidify and form a protective covering, however this will remove the fibre’s flexibility, resulting in a ‘hard’ seating surface

Neat’s-foot oil rots leather is just a myth, any oil will trap moisture in the stitching, which will cause them to fray and rot. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will compromise the resin binder system and delaminate from the hide releasing its adhesive bond, and it will be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering

If oil is allowed to permeate any micro fissures in the leather or via the stitching it will travel laterally compromising the resin binder system which will delaminate from the hide releasing its adhesive bond. It will then be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering

Leather is very dynamic with respect to its moisture content; the leather hides needs to be kept supple. The purpose of rehydration is to restore moisture lost through evaporation, so whatever the surface finish, it has to allow the movement of moisture back and forth (evaporation and hydration). The liquoring (fats and oils) that are put into the leather during the tanning process do not dry out of the leather in normal circumstances so therefore do not need replacing.

Modern automotive leather upholstery use a completely different tanning  processes and finishing system, utilizing advanced polymers and chemicals and as a consequence  they do not need to be treated with aftercare products containing oils.

Leather Conditioning 

Modern automotive finished leather upholstery used by 95% of OEM is a multi strata covering over the leather hide; pigmentation (colour) and an abrasion resistant urethane. Finished leather s only requirement is to be kept clean and protected, urethane doesn’t require conditioning

 The following are factual details that leather care manufacturers would rather you didn’t know.

When leather tanners talk about conditioning leather they are referring to re-hydration; not the replenishment or replacement of the fat liquoring oils and waxes. The only 'conditioning' required for finished leather upholstery is hydration; oil-based products cannot permeate the finish leather (urethane pigmentation and / or covering) that is used in 95% plus of modern automobiles.

Modern leather needs to be kept hydrated with moisture to ensure the leather remains flexible and maintains its soft tactile feel. This is done by regularly wiping the surface with a damp 100% cotton micro fibre towel and by using aqueous (water- based) leather care products. There is no reason to use oil-based leather care products to condition or feed leather hides

Aqueous (water- based) products are able to permeate deep into the hide, unlike oil, due to its larger particles, whereas water particles are smaller than both oil and the molecules of urethane, which enables aqueous (water- based) products to permeate and provide hydration, which is essential for suppleness recovery.

Particulate size - you can tell how small the emulsion droplets are and in some cases how concentrated an emulsion is by its colour. Opaque white emulsions typically have a large particle size, while faintly opaque or pearlescent emulsions typically have a small particle size approaching 1µ or less.

           Water - unlike other organic or hydrocarbon-based solvents, is non-flammable, odourless, non-toxic and non-sensitizing to the skin and it doesn’t impart a greasy or tacky feel to the surface of the leather

I have discussed this issue with many people in both the leather tanning and leather care products industry and some specialised industrial chemists who have worked in the leather manufacture and care industry for 35 plus years.

As specialists in leather care they had a much better understanding of what the ideal product is for maintaining finished leather surface used in automotive leather upholstery and i asked the following questions.  

We discussed the product s that are currently being used and the consensus was that many of the products simply were not suitable for the current finishes used for automotive leather

I looked at a detailing care product vendor site and found nine pages of leather care products, mostly expensive oil-based leather ‘conditioners’  this could be the reason they ignore an appropriate care product for the upholstery  material actually used for automotive (finished leather) upholstery. They are in business to make money

1. How much oil-based conditioner or ‘fat liquoring’ will permeate the urethane top coat on a sealed pigmented leather hide? Chrome tanned leather hide is sealed at the tannery and then pigmented; what could a conditioner do for the hide?

2. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will travel laterally compromising the resin binder system which will delaminate from the hide releasing its adhesive bond. It will then be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering

3. The complex tanning process of chromed tanned hides results in the fat liquoring and oils necessary to keep the hide soft and pliable being locked in, this is further sealed by a durable polyethylene covering to protect the hide from abrasion from clothing as well as the dust / dirt introduced by the vehicle’s AC system.

4. The complaint that most leather conditioners are "greasy" is typically attributable to the use of Lanolin. On most leather conditioners the containers label warns against its use on steering wheels as it will make them slippery and unsafe. The oils cannot permeate the leather and therefore remain on the surface; the same thing will apply to seating surfaces; the problem will be exasperated as the oil will attract dirt/grime to the surface

Many so called leather conditioners utilize chemical solvents in order to facilitate penetration of the oils into the urethane covering or the pigmented leather. Most covered leather finishes are water -based and so any solvent or alcohol can begin to cut through them, even if you go over it and you see no colour come off, you have probably compromised the clear protective top coat and possibly the leather’s pigmentation (colour).

Solvents will soften the protective covering, which can get tacky very quickly, attracting abrasive dust/dirt and will eventually wear through as it does not have the durability found in the topcoat. What happens when the solvents vaporise - polish and many surface protection products are formulated with oils to enhance the surface or to nourish leather surfaces, neither of which is necessary?

Not all conditioners are alike; some are aqueous (water- based) as opposed to oil-based. Some contains about 90% water, when applied to the leather surface, it appears to “soak in” (hydration) leaving only a very thin film of oil to benefit the surface lubrication (driver or passenger entry / exit).

A urethanes fibre structure will stretch in all directions with no particular grain or stress pattern. The urethane surface coating will  not withstand multi directional stress,  however, and when it’s flexed or stretched continuously in the same place the surface coating develops minute cracks. If oil is allowed to permeate any micro fissures in the leather or via the stitching it will compromise the resin binder system and delaminate from the hide releasing its adhesive bond, and it will be able to move in a different direction from the hide, which will result in surface fissures and cracking, further compounding the problem eventually leading to the subsequent replacement of the protective covering

In summary, an aqueous micro emulsion is readily absorbed into the fibres and provides lasting and effective lubrication without migration, while re-hydration leaves leather feeling silky

Three Step Leather Care

Simple cleaning, hydration and protection are the three steps that will prolong the life of finished leather;

Urethane doesn’t require conditioning or rejuvenation; always keep in mind that you’re dealing with the finished coating on the leather and not with the leather hide itself

Clean - there are two cleaning-related factors that can cause your leather to wear prematurely.  The first is dirt, and the second is oil, combined they become very abrasive, as dirt / grit and subsequent friction cause the finish to wear

Hydrated – when leather tanner’s talk about conditioning leather they are referring to its moisture content, re-hydration is used to restore or maintain fluid balance (transpiration and evaporation of moisture); not the replenishment or replacement of the fat liquoring, oils and / or waxes.

Protected - is essential as it will protect the surface finish, without hindering transpiration, while acting  as a sacrificial layer; this way you are not actually cleaning the Leather's original surface, but cleaning from the surface of the protection. It also makes dirt easier to clean off

Ultra violet (UV) protection - 303® Aerospace Protectant will provide invaluable UV-B against photosynthesis (fading) protection; especially in a roadster or convertible vehicle

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