If low-quality paper is used, it can yellow and degrade due to residual acid in the untreated pulp; in the worst case, old copies can literally crumble into small particles when handled. High-quality xerographic copies on acid-free paper can last as long as typewritten or handwritten documents on the same paper. However, xerographic copies are vulnerable to undesirable toner transfer if they are stored in direct contact or close proximity to plasticizers, which are present in looseleaf binders made with PVC.