Puppy Bumper - Reflective Glow Pups Bumpers - Make your pup TOO FAT to fit through the rails... and FIND him in the dark! Hi-Viz yellow material with reflective piping around the outer edge Dog's collar threads through loops to stay secure Light, comfortable, machine wash and dry. Measure the dogs neck where its collar rests naturally. You should be able to put two fingers between the measuring tape and the dogs neck. Having the correct size is important for the Puppy Bumper to be comfortable and effective for your dog