Keep in mind that the aging and yellowing of record jackets are a function of effects of light and humidity over time, not so much the absence of a plastic sleeve. The plastic sleeve principally serves to protect from wear (rubbing, scuffing, etc) and to keep out dust and other contaminants.
Sleeves with a foldover resealable flap will provide the best dust and contaminant protection, but the trade-off is a bit more trouble extracting and replacing the LP if one also actively plays the vinyl in one's collection.
I've found all of the current "crystal clear polypropylene" outer sleeves offered by Sleeve City to be excellent sleeves. For my purposes, I've come to prefer the "Ultimate" 2.5mm sleeves in both regular and box set sizes. Unlike other polypropylene sleeves sold elsewhere, these really seem to not cloud with age but do stay completely clear, giving a very nice appearance and allowing one to more easily read the spines of the records on the shelves.
Here's the link to the outer sleeves offered by Sleeve City:
http://www.sleevetown.com/lp-sleeves-outer.shtml
.
Sleeves with a foldover resealable flap will provide the best dust and contaminant protection, but the trade-off is a bit more trouble extracting and replacing the LP if one also actively plays the vinyl in one's collection.
I've found all of the current "crystal clear polypropylene" outer sleeves offered by Sleeve City to be excellent sleeves. For my purposes, I've come to prefer the "Ultimate" 2.5mm sleeves in both regular and box set sizes. Unlike other polypropylene sleeves sold elsewhere, these really seem to not cloud with age but do stay completely clear, giving a very nice appearance and allowing one to more easily read the spines of the records on the shelves.
Here's the link to the outer sleeves offered by Sleeve City:
http://www.sleevetown.com/lp-sleeves-outer.shtml
.