Personally I do not believe in imprinting foals. Handling yes--when the foal is born I treat the stump, check to see if it is filly or colt, and watch to see if the foal starts nursing, and if assistance is needed with that then I assist. That's it. After that, the foals are handled daily--handled as in caught, rubbed/scratched, talked to--and they become very friendly very quickly. When I start halter training them at 3 to 4 weeks there's never a problem putting a halter on them. I usually clip the foals some once the weather turns hot, and I just take the cordless clippers out into the corral & clip there. I do not have to halter the foal nor even restrain it. Last year when I went out to clip all four foals crowded around, trying to to tell me CLIP ME, CLIP ME, no, MEEE!
I fail to see how a foal could be any quieter, friendlier or more agreeable to work with--and I just do not see any need to be "imprinting" the new foals--holding them down, running clippers all over them, sticking my fingers in their mouths...