The three grades
- Full grain - the top layer with the natural grain intact and only a light finish. The most durable and the most expensive. Natural marks are part of the look, not a defect.
- Top grain - the top layer, lightly sanded to remove marks and then finished. More uniform, slightly less breathable.
- Split leather - the lower layer, usually embossed with a grain pattern and coated. Cheapest, least durable, and the source of most 'this is not real leather' disputes.
Bonded and 'PU leather'
Bonded leather is shredded leather fibre glued to a backing. PU leather is a polyurethane coating on fabric or split. Both can be perfectly good for a price-driven market - but they must never be described as full grain.
How to write a safe specification
Name the grade, the thickness in millimetres, the finish and the origin. Add a clause requiring a 15 cm x 15 cm sample to be sealed and kept by both sides. If a dispute arises, you compare the shipment against that sealed sample instead of arguing about adjectives.
Thickness in practice
For a residential sofa, 1.2 to 1.4 mm is the normal range. Below 1.0 mm the leather will stretch at the seat front within a year. For hotel and contract projects, specify 1.4 mm or above.