I use the BagsUnlimited.com POLYPROPYLENE 12" sleeve with the 1-1/2" RESEAL Flap. Product number SPPLP1234R is 12-3/4 x 12-3/4, which is slightly loose on normal albums and just big enough for heavy gatefold lp's. Very reasonably priced if you buy 500 or more.
Best Outer Sleeves for LPs
Is there a recommended type of plastic sleeve to protect valuable record covers from aging, yellowing, etc? I can buy them very inexpensively from the Princeton Record Exchange, but wondered whether they would have the desired effect. I've also seen poypropylene sleeves sold online at Sleeve City. Any recommendations? Thanks very much!