Two pets, two carriers, one frame. This stroller stacks a pair of pet carriers on a single chassis, and each one detaches to be used on its own, which is where the four functions come from: a double pet stroller on the wheels, a carrier bag by the handle, a pet crate set down indoors, and a car seat carrier belted into a vehicle.Each carrier measures 13 by 14 by 22.5 inches and loads up to 17 pounds, so this is a setup for two small pets rather than one large one. Inside each, a soft comfortable cushion gives the animal something to settle on, and a safety belt clips in to prevent a pet running out the moment a door is opened. Mesh windows let both breathe fresh air and stay visible on the move.The running gear suits real pavements. EVA wheels handle all kinds of road surfaces without the harshness of hard plastic, and one-foot-stop brakes on the rear wheels bring the whole thing to an immediate stop. Folding takes seconds, collapsing the 20 by 27 by 41.5 inch stroller down to 20 by 11 by 33.5 inches for storage or a car trunk.Materials are chosen for daily use. A sturdy steel frame carries the load without flexing, and the selected Oxford fabric is wear-resistant, tear-resistant, and waterproof, so a wet walk does not soak through to the cushions. A side pocket takes small items, an ergonomic grip handle keeps pushing comfortable, and the whole 17.5 pound stroller ships in one box in beige with a user manual.