Finished Leathers :
Top-Grain : Top-grain leather has a pigmented resin coating, to provide stain and wear resistance. Because these hides are generally free of major scarring or other unsightly characteristics, nothing is done to the epidermal layer. So, its natural grain pattern is evident.
It’s not easy to determine if your leather is top-grain. One factor may be price. Because top-grain leather is typically free of unsightly scarring, it is more expensive. And because all skin growth is from the inside outward, the most mature, tightly-woven, and most durable layer is the outer layer (the top-grain). They come in any color, and, thanks to special coloring effects, can simulate the look of the more natural, organic appearance of unfinished leathers. They don't warm to your body temperature as fast as unfinished leathers, neither will they wick away (absorb) body moisture as readily. However, the combination of a protective color coating and the natural durability of the hide's epidermal layer will afford long-term durability with minimal care. In a high-use environment (like an active household, or a commercial placement), this is the type of leather that will offer the best performance over time. While it's not bullet proof, you can expect 20 or more years of use, if properly maintained.
Corrected Top-Grain : Corrected top-grain leather has its epidermis abraded (sanded) to remove significant scarring or other unsightly characteristics. This weakens the material, as the epidermis contains the most mature, structurally stable fibers. The hides will either be very smooth (no grain pattern), or have a grain pattern embossed onto them, and then are coated with a pigmented resin. Like top-grain leathers, corrected leathers can have print effects that make them more natural-looking.
The degree to which the epidermal layer has been compromised through sanding determines the long-term viability of corrected top-grain leather. It is the outer 1 millimeter of the hide that provides the most significant tensile strength. As you erode that layer through sanding, and go deeper into the skin, you end up with progressively weaker leather. Corrected top-grain leather performs well on desk or table tops, or other applications where the tensile or flex strength of the leather is not challenged over time.
Splits : Split hides get their name from the process in which the top-grain (upper) section is cut away (split) from the suede (lower) section, rendering two separate hides from the initial one. As noted in the top-grain section, the vast majority of leather’s strength is in the outer layer. Therefore, splits are a much weaker leather than top-grain, and will not stand-up well over time, particularly in active households or commercial placement.
The inner layer of the top-grain hide is suede. The corresponding outer layer of a split is also suede. Thirty years ago the split was considered waste. Some clever engineers came up with the idea of putting an resin coating over the split’s top surface, laying down and encapsulating all of those loose fibers, to create a smooth surface. Then, a synthetic grain pattern is stamped onto it, and finally, it is heavily coated with a pigmented resin to seal and color it. This leather is generally hard, cold, and lacks durability.
Bi-Cast : In the true sense of the word, this is NOT leather. Bi-cast leather is to real leather as pressed wood is to real wood. It is a manufactured product made from either: 1). Chopped up leather fibers mixed with an epoxy, or, 2). a split hide. It is then coated with a heavy urethane film. The dominant strength of this product is the urethane coating, not the underlying “leather.” This is a problematic material. It presents well, typically in a rich dark brown color, but has none of the true durability or aesthetic characteristics of real leather. If the phrase “buyer-beware” ever applied, it certainly applies to bi-cast. To learn more read this post.
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