I told you I've turned my old athletic shoes into indoor "slippers". I need support for my feet even for casual use and can't wear cheap slippers. I priced high-quality slippers, and those were more expensive than I'd ask for as a gift.
So, this is one of the fleece inserts. They're sold in pairs and either cut to fit or sized. Some come with arch support or extra foam cushioning. Mine are sized so no trimming required. For a shoe insert, you take the old insole out and just place the fleece insert in its place. If your shoe is extra roomy, the insert may fit inside on top of the original insole. For a boot insert, if the boot is roomy, you simply slide the fleece insert into the boot.
I'm using these to make my shoes comfy-cozy (with or without socks) to wear as slippers. Many folks, though, use shearling inserts to make favorite shoes or boots warmer in winter. Wool fleece does a good job regulating temperature to keep feet from freezing in cold weather. It's recommended to hand-wash and line dry shearling fleece inserts periodically.
In reading reviews online, I discovered that many folks buy these to make their slippers warmer or more cushioned. I think that if one has closed-back slippers with worn fleece insoles, these would refurb the slippers for a lot less than buying a new pair. Price wise, most of what I found online were under $20 for a pair. I'd never heard of these before finding them in a catalog in fall, so I thought I'd share my info.
As for my pair of new "slippers", I'm really enjoying the fleece insoles. Soft and warm -- what's not to love?