I've made my own--had a foal born into -35 weather and found that the blankets and liners (fleece) that I had on hand just weren't warm enough. So, while I had the baby in the house warming her up the first night I got busy & cut up an old wool hudson bay blanket--made 3 foal blankets out of it, each one a little larger than the one before it. Instead of a pattern I just used the foal as a guide--cut out the basic blanket, put it on her, cut it a little more...and ended up with a perfect fit. I sewed it up by hand real quick & she had a nice warm blanket on the spot. So, I'm not help as to pattern....
I do prefer the closed front blankets for the foals, and I put a wide belly band on, with velcro to fasten it in place--I used fleece for the belly band. Since I was using the wool fabric & it was quite soft & so drapes nicely, I cut the back of the blankets very generously, rather than shaped it like a typical horse blanket--these foal blankets are cut longer so they come back over the tail & kind of drape over/around the hindquarters--no problem for the foal to lift its tail to poop, yet the blanket drapes down around the hindquarters for extra warmth. These blankets just seem to wrap right around the foal--they're warm & snug & offer no way for baby to get its legs stuck in the front of the blanket or in the belly band (a big concern with some of the blankets I've seen on the market!)
