Machine Washable For your convenience, this underlay is machine washable on a wool cycle, so you can keep it clean and fresh for a healthy night’s sleep. This luxurious underlay is made with the highest grade Merino wool, which is renowned for its superior comfort and quality. It is fully reversible for summer or winter, and has a deep wall skirt that suits high mattresses up to 40 cm. It is also machine washable on a wool cycle.