Abstract: The paint tray liner apparatus provides removable fit to an existing paint tray, thereby providing a disposable liner. Flexible sides are collapsible and the liner bottom relatively rigid. The collapsible sides provide for reduced space storage of the apparatus, whether prior to use or after when discarded. The collapsible sides each has an inner panel spaced apart from an outer panel. Each inner and outer panel is connected by the continuous shelf. The side panels thereby fit the sides of a paint tray, with the apparatus tray bottom against a paint tray bottom.