The right cover is a crucial part of any nappy system to prevent moisture escaping from the nappy and onto your baby's clothes. You will only need 3 or 4 wraps at any one time as they only need changing at the end of the day or in the morning after being worn all night.
If you are still at the dazed and confused stage of cloth nappydom, then let me point you in the direction of the Motherease Rikki and Airflow wraps. Both are made of PUL ( a laminated fabric) that is both breathable and water-proof. These wraps are soft, trouble-free, won't wick or leave nasty red-marks on your baby's skin. You can use these wraps day and night.
We also stock some lovely fleece and wool wraps which are a bit more breathable and great for nightime.
For more info about the different types of wraps and when to use them, see the Cloth nappies made simple section of the site.