The Kaytee CritterTrail Fun-nel Loop-D-Loop Accessory Kit is a medium-sized tank topper designed for small animals like hamsters and mice. Made of plastic in a blue color, this single-tier habitat adds an extra level of entertainment and complexity to the critter's living space. The Fun-nel Loop-D-Loop Accessory Kit is a popular choice for pet owners looking to enhance their small animal's habitat with a fun and engaging addition.