This mini horse halter is made from 1" MFP (Poly) which has some advantages over typical nylon halters… it is soft and pliable being very comfortable for the animal, it is stretch and water resistant, UV resistant therefore won't fade in the sun as nylon is quick to do. It is a soft flexible material but very sturdy and reliable with a 600 lb tensile strength. The medium size will fit the typical adult mini. Medium: Nose = 16 inches; Crown (measured from the noseband area up and around the poll and down to the noseband area on the opposite side) = 23 to 28 inches. Large: nose = 19 inches; Crown = 24 to 29 inches. A QUICK MEASURE AROUND WHERE THE NOSEBAND SHOULD LAY WILL GIVE A GOOD INDICATION OF WHETHER A MEDIUM OR A LARGE WILL LIKELY WORK BEST FOR YOUR ANIMAL.