When we had our aircraft re upholstered, we looked at costs. It was cheaper to use leather rather than the approved cloth materials. This is because the cloth has to be non flammable and not give off toxic fumes. Leather doesn't suffer either of these problems.
From memory the reupholstering was in our maintenance records with all the details of who did it and what was used, your logbooks should show this.
If its not in your records perhaps someone has reupholstered your aircraft 'unofficially' and perhaps used the wrong material.
ZA