@lewm: The Vinyl Storage Solutions Double-Pocket sleeve is made of 4mil cast polypropylene, but since it is made of 3 sheets of the plastic, the sleeve adds 12mil to the thickness of standard (non-gatefold jacketed) LP’s. As for the added space needed due to the LP being stored outside the cardboard jacket, with no LP inside it the jacket itself takes up less space than it does with an LP inside it (the front and pack of the jacket compress against each other). Plus, with gatefold covers I use the double-pocket sleeve with the pocket for the LP inside the gatefold, so no thickness is added to the LP/jacket/outer sleeve. So yes, use of the VSS double-pocket sleeve does result in more space required for the same number of LP’s, but I don't think anywhere near double.
@whart: 45 RPM Audiophile’s name is Mike Ludwig, and yes he’s the Mike in Germany. I quickly learned that while we are both audiophiles, our musical tastes are vastly different. In one of his reviews of a group of Vinyl Me, Please LP’s he received, he panned Iris DeMent’s My Life album, one of my very favorites (Merle Haggard loved it too, recording her song "No Time To Cry" himself). That was pretty much the end of Michael Ludwig for me.
By the way, VSS also offers inner sleeves, in a number of different versions (2mil, 3mil, with and without flaps, both flat and round bottoms, 100% clear and also with a "rice" paper side, etc.). Most are very similar to the MoFi inner sleeves (but thicker. I believe the MoFi’s are 1mm thick), some cheaper in price ($7 for a 25-pk. of the round bottomed 2mil sleeve, $12 for a 25-pk. of the 2mil rice paper sleeve, $14 for the 3mil). VSS orders of $55 U.S. or greater ship free.