When it comes to vehicle leather upholstery care information, there are plenty of myths and very few real facts. I hope this technical article will provide you with enough 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.



Automotive finished 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 protective finish.



The urethane (Ethyl carbamate) used for automotive finished leather is a non- expanded vinyl 90% polyurethane and 10% plasticisers and 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 (leather hide).



The urethane although very resilient to abrasion wear from entering and exiting the vehicle, by using additives it still maintains its physical properties like flexibility, tactile hand and its patina



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, which usually includes additives to give it a soft feel and a limited amount of ‘slide’ as the final stage of the finishing process.



Oils from the body or other sources attack the polyurethane softening the finish to the point of it being able to be peeled off. Improper cleaning, especially solvent-based products attack the plasticisers drying the finish, causing it to crack



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 transpiration (evaporation and hydration) the passage of water vapour through a membrane or micro pore, they are not sealed per se as some chemicals penetrate it easily; others stay on top dependent upon their molecule size.



a) Finished leather - unless a Premium Leather option was purchased the type of leather upholstery used by 95% of OEM is a multi stratum covering over the leather hide; the top strata is the surface pigmentation (colour) and an abrasion resistant urethane.



b) Covered leather – see (a) above



c) Pigmented leather – a spray-on colouring applied to a leather surface. More often pigmentation is applied to a urethane, which provides an even colour to the upholstery as well as abrasion resistance



d) Aniline (more correctly Micro Pigment) – aniline leather is very rarely used for vehicle upholstery. Micro pigment leather is protected by a micro-thin urethane, which incorporates pigmented (colour) hence the name, sometimes perforations are added.



Other ‘aniline leather’ (Milano, Silk Nappa, Valcona (Audi) Boston, Baseball, Dakota, Montana, (BMW) Chaparral, and the leather used in a Range Rover Vogue are examples of micro pigment leather. A thin, transparent dye is added to an opaque medium, the opacity remains, although some colour is added



e) Micro Pigment – see (d) above



3-Step Leather Care



1. 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



2. 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.



3. Protected - is essential as it will protect the surface finish 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



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



Relevant Articles



1. “Reference sources and bibliography used for leather articles” - http://www.autopia.org/forum/autopia...ml#post1474865



2. “Leather Surface Identification” - http://www.autopia.org/forum/guide-d...ml#post1451654



3. “Proper Finished Leather Cleaning and Care” - http://www.autopia.org/forum/guide-d...ning-care.html