Wool diaper covers are great because this natural fiber stays cool in summer and warm in winter. A wool diaper cover is very absorbent and is often recommended for nighttime use, when leaks are common. The natural lanolin in wool creates a waterproof barricade, yet it is still breathable. Wool is also known to be very durable and sturdy, but can be a little bulkier than other diaper covers. Many people recommend hand washing wool diaper covers, but some are able to be put on the gentle cycle in your washing machine.