These storage bins are made of durable and safe PP (polypropylene) that is strong and waterproof. The sturdy construction is designed to keep the bins in shape for long term use.The storage box has a collapsible design that allows it to fold flat when not in use, making it easy to save space. Both the front and top lids can be opened for easy storage and removal of contents. Four invisible rollers are built into the bottom for easy movement during cleaning. It can be used in combination to stack boxes tightly together. The top lid has four grooves that match the wheels, so you don't have to worry about the storage boxes falling off when stacked. Features moisture, dust, and two-way closure.Great for closets, bookshelves, dorm rooms, closets, nurseries, attics, laundry rooms, bedrooms, RV storage, lingerie or toy organization, and more.