I found out the same.
Midwest Winters mean the occasional Polar Vortex with Sub-Zero temps.
Even so, I rarely blanket my Herd of 3:
20yo Hackney Pony
18yo TWH
6yo mini
When I do, blankets are waterproof turnouts with nylon lining, 180g fill.
I got each a waterproof sheet (no fill), used them once & said Heckwiddit!
Horses are turned out w/access to stalls & if they want to come in from the rain, they can.
For horse & pony I got Kodiak brand turnouts from Horseloverz.
Going on 2yrs & look brand new, though used so rarely I’m sure that helps.
For the mini, a Tough-1 blanket is 3yrs old & sadly outgrown. He was 2-1/2 when I bought it & now shows Plumber’s Butt :o