Alter-nappa leather is a type of faux leather. Faux leather is used as an alternative to genuine animal leather and is also known by other names such as vegan or vegetarian leather. Specifically, "alter-nappa" is the name used by Stella McCartney for the type of faux leather used in her shoes and bags. The name originates from Napa Leather, a soft leather created by a tanner Emanuel Manasse in Napa City, California in the late 1800s.
Alter-nappa leather is made from a combination of polyester and polyurethane. Polyester is a textile made from a type of plastic. More precisely, it is "made up of molecular polymers associated with the ester group of chemical compounds," which is how the name 'polyester' is derived. Polyurethane is a highly customizable plastic that can exist in many forms, making it rigid or flexible. Alter-nappa leather also contains a recycled polyester backing and a coating made from over 50% vegetable oil.
There is widespread debate in the fashion industry as to whether the use of synthetic materials like faux leather is more sustainable than animal leather. Some argue that animal leather is better material because it is organic, biodegradable, and a renewable resource, all of which are benefits to the environment. Others argue animal leather should not be used because of the cruel treatment towards animals. The Stella McCartney website acknowledges that synthetic materials are not without their own environmental concerns and believes that using recycled and bio-based materials with lessen their detrimental impact.