The mesh eye-wear is made of breathable UV mesh (similar to a fly mask for horses) that filters out 50-60% of UV rays, while allowing for all day wear. The mesh eye-wear is flexible and will protect your pet from UV rays, not hard foreign objects (ie sticks, rocks, brush, ect). It doesn't impair your dog's 270 degrees of vision (not 180 like humans). Elastic and adjustable straps hold the eye-wear in place comfortably. Available in 4 sizes and 2 colors. Size Weight of Dog, Head Strap and Frame Chin Strap, Breed Example XS 1 - 10 lbs 11.5-15 inches 9-10 inches .5 - 5 kgs 29-38 cm 23-25 cm Breed example: Chihuahua, Pom Small 9 - 25 lbs 13-16 inches 12-14 inches 4 - 12 kgs 33-41cm 31-36cm Breed example: Beagle, Westie, Jack Russell Medium 20 - 60 lbs 18-23 inches 15-18 inches 9 - 27 kgs 46-59 cm 38-46cm Breed example: Aussie, Border Collie Large 50 - 100 lbs 20-24 inches 19-22 inches 22 - 45 kgs 51-61 cm 48-60 cm Breed example: German Shepherd, Labrador Retriever Size Length* Height* XS 6in/15cm 2.5in/6.4cm SM 7.5in/19cm 3.5in/9cm MD 9.5in/24cm 4in/10cm LG 12in/30.5cm 6in/15cm *Length is the measurement from one corner of the frame to the other (corner of eye to corner of eye). *Height is the measurement of the eye portion of mesh.