The CheckOutStore 33 1/3 Polylined Paper Record Sleeves are a archival quality product. We use high quality premium 24# paper lined with acid-free polypropylene. Manufacturer: CheckOutStore Part Number: COSRS33PPBLK Specification: ** Category: Record Inner Sleeves ** Color: Black ** Size: 12" ** Style: LP ** Type: Square Corners ** Material: Polylined ** Measurement: 308mm x 305mm (12 1/8 x 12 inches)