I assume we are talking about pigmented leathers.
So technically it’s two layers – the finishes comprises of the colorcoat and the topcoat; the structure is protein fibers with other leather constituents and it’s the level of fatliquor that will determine whether the leather structure will crack or not.
Why do pigment cracks, is the plasticizer in the binder that holds the pigment give way when it is stretch, compress or flex – plasticizer do diminish as VOC (volatile organic compound) through excess heat, alcohol or alkaline cleaners; resulting in difference in elasticity between the structure grain surface.
The thickness of the leather structure cracks is due to the diminishing fatliquor (lifeblood of leathers); resulting in the fibrils being stick together stiff and when flexes cracks.
Micro cracks are supposed to develop on urethane finishes to allow for the leather to breath as typically found in Micro-pigmented / semi-aniline leathers.
Napa pigmented leathers is some luxury models uses Nitrocellulose as binders for the pigment color; thus forms “discontinuous” film that breaths easily and is more comfortable to seat; these discontinuous film develops quickly when the colorcoat is applied with the matching topcoat.
Leathers that breaths are the high-end type; versus leather that is overly protected is the low-end type closer to vinyl.
So it’s recommended not to over protect the finish that makes it suffocating to the leather structure that leads to cracking to the structure; it also makes rejuvenating the leather structure much more difficult.
You will see more and more leather perforated for this reason – the utility of the leather depends on this thickness of leather and the fatliquor needs to replenish on a regular basis to keep it soft, strong and supple.
Roger Koh
info@leatherdoctor.org