Wool diaper covers are great because this natural fiber stays cool in summer and warm in winter. Wool 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.