These are Square Deal Recordings & Supplies Brand 12" Polylined Inner Sleeves. These sleeves measure 12-1/8" x 12" with a 1/4" lip (308.12mm x 304.8mm with a 6.35mm lip). They are made from heavy weight, 20# paper with a high-density polyethylene lamination. This is a much stronger material and is more anti-static than traditional, low-density polyethylene sleeves.The difference is in the way that the lining is put on to the sleeves. Traditionally, 12" polylined sleeves use a gluing process. When the sleeves are glued, there is always a visible glue lining on the inside of the sleeve and down both sides along the edge - sometimes it's subtle, sometimes it's really obvious. If the sleeves aren't glued up high enough, then the record can get caught between the paper and the plastic, ripping the sleeve. The plastic is glued on one side and all along the top edge. The side gluing does not make a complete bag, but one that is opened on the glued side, creating a path for paper dust from the paper sleeve. If the plastic isn't glued down inside the entire sleeve, then the plastic can get caught and pulled out with the record.Square Deal's premium sleeves are made by laminating the paper with the plastic before the sleeves are folded. While it looks like only the window is covered by the plastic, the plastic is actually it's own layer that's laminated onto the paper. This creates a glueless and seamless, pristine sleeve that offers the same better protection without any of the downsides that can happen with a traditional polylined sleeve.**WARNING: The first use of these sleeves, you will notice a slight tack to the outside center window. This tack will disappear after the first time you remove the sleeve from the record jacket.**