Thundershirt Heather Grey, Medium keeps dogs calm during thunderstorms, fireworks, or helps with separation anxiety, travel, crate training, and more by creating gentle, constant pressure. Pressure has a calming effect on the nervous system and helps relieve anxiety. Thundershirts are a well-designed, inexpensive pressure wrap for dog anxiety. Size M is for dogs weighing 26-40 lbs. Please note that this product may only ship via UPS dimensional weight, which is above its actual weight.