Like nappies, covers (also known as 'wraps') come in all shapes and sizes. 

Quality covers are largely manufactured from breathable, soft and durable fabrics such as PUL (polyurethane laminated polyester) and minky, a soft, velvety polyester finish. These covers allow air to circulate while keeping wetness away from your baby's clothes and bedding.

An a more breathable option, fleece covers (incluing Malden Mills WindPro, microfleece and polar fleece)  work on the basis of evaporation.

With sufficient air circulation around the cover, wetness is evaporated out through the cover, thus extending the absorption of your nappy underneath.  Fleece is great for overnight, or any periods of extended wear.  Sugar Peas fleece covers are high quality and really slim fitting.  Bear Bottoms offer wonderful breathable protection over even the most heavily boosted night nappy.

Even more breathable, thermo regulating (cool in summer, warm in winter), and self-cleaning, are wool covers.

Wool has a unique combination of three properties, breathability, absorption and water resistance.  Machine or hand knit, wool  covers are commonly known as soakers or longies (full leg length lanolised woolen clothing that doubles as a nappy cover).

All nappy covers can  be fastened with either snap buttons (Motherease Air Flow,  Sugar Peas) or hook and loop -Velcro, Aplix and touchtape  (Motherease Rikki, Thirsties, and Bummis), either at the front or sides. 

To some extent, hook and loop fastening offers wide adjustment in ftting, though it can also add bulk and is easier for inquisitive toddlers to remove.  Covers like the Dancing Bears Bear Bottoms and Bummis Whisper Pants are a pull up style. 

PUL is great for everyday wear, wool is wonderful for overnights, and fleece is really easy to care for  and a great alternative to either style. 

If you are using fitted nappies, Nurture Nappies recommends4-6  covers for day wear, and a wool or fleece cover for overnight.