[QUOTE=Magicboy;8949004]
What’s the name of that Smartpak ap?[/QUOTE]
SmartBlanket
[QUOTE=Kodidog763;8948529]
My horses (Thoroughbreds) are unclipped and out 24/7 in Minnesota (so we get “real” winter) with access to a shelter. Mine get sheets if we are going to have sleet or wet snow. They get heavy blankets if we are going to be below zero for a period of time. Otherwise mine go naked. :)[/QUOTE]
I pretty much follow this regime.
Midwest US, so Polar Vortex is in my vocabulary 
My horses live out with access to stalls if they want.
They rarely want.
I own midweight blankets - 200g fill - & blanket only when we’ve had such heavy snowfall that they are wet through on their backs.
Bellies are usually dry & warm, but blankets go on & come off as soon as the backs are dry.
When temps stay below the teens for days on end, I will blanket, but prefer to let them go without. The insulating layer of air trapped in their coats does a better job, IMO
FWIW, I had a WB who was bred in Queensland, Australia < similar climate to FL, was imported & spent 6yrs in FL then came to live with me in the frigid Midwest.
He arrived - showslick - in December and in the 6yrs I had him never really grew more than a plushy Winter coat. He was perfectly fine unblanketed in all weather.
Let your horses tell you when they need a blanket.
Ear-tips, bellies & briskets warm to the touch?
They are fine nekkid.
Snow piled on their backs, but not melting?
They do not need blanketing.
Shivering, huddled together, tails clamped - in general looking unhappy?
Put on a blanket.
I find the midweight does the job w/o needing to add layers or change blankets.
Only lately have I considered adding waterproof sheets
But that is mostly my guilt at seeing them out on the rain, soaked nearly through on their backs.
They still test warm & don’t seem to mind the wet, preferring to stay out grazing even if nice, tasty hay is in their stalls.
Footnote:
Have you noticed they seem to have a natural flow pattern of water draining down their backs but not getting their bellies wet?
It depends on the horse, their living conditions and, where I live, the rest of the weather details besides temp - wind and rain/damp. We don’t get many clear days in the winter, there is a bone-chilling damp most of the time, and pretty constant wind or at least breezy.
The smartblanket app is usually close to right for my QH gelding, my WB gelding sometimes will need a light fill turnout when it says just a sheet, and my mare usually needs a medium when it says just a sheet.
My horses live out 24/7 with run-in on the back of the barn. When my WB gelding was boarded and in a barn at night with doors closed and 10 other horses generating body heat, he lived in a rain sheet almost all winter.
My 25 yo mare I blanket heavier than the other two, because once she gets cold it’s very difficult to get her warm again. She’s in a mid-weight blanket right now, with temps in the low 40s at night and mid-40s in the day, breezy and damp weather.
If it gets below about 15 degrees she has a hard time staying warm even bundled up with a liner, heavyweight blanket and a sheet over that. Last year when it was 9 degrees and windy for a couple of days, with the wind blowing the “wrong way” straight through the shelter, I also put shipping boots on her (a suggestion of my trainer - it really worked) and leave one of the halogen lights on in the run-in. She stands with her face close to the light all night, poor girl. Reading this thread, I think I should get her a hood for those really cold nights.
