No expense of washing and disinfecting. Made of coated pressboard. Great for kennels, hospitals and home. Excellent for travel. Top opening is listed below. Small 1000 pack-5 1/4"L x 3 1/2"W x 1 3/8" H Medium 1000 pack- 6" L x 4 3/4"W x 1 1/2"H Large 500 pack- 7 3/4" x 5 1/2" W x 1 3/4" H X-Large 500 pack-9 1/2"L x 6 1/2"W x 2 5/8" Hw