This is what I plan on doing, as suggested at OSDS:
|Pre-Washing Instructions: Wool fabrics need to be "felted" before using to sew a diaper cover. Using a lanolin wool wash such as Eucalan®, (Do NOT use regular detergents with wool!) wash your wool fabric on hot and dry on hot. Repeat the process at least once. The hot temperature combined with the cold rinse and agitation of the washing machine and dryer will felt the fabric, it will look thicker and bumpier when it comes out of the dryer.|
The shrinking process causes the fibers to felt up, filling in holes and appearing thicker & more dense when you are finished. Wool can shrink unevenly, and sometimes the edges get a bit wavy. Be sure to order enough to allow for shrinkage, you can lose several inches during the felting process. One yard of wool jersey is seldom enough to work with once felted.
Wash and Care for Wool Covers: Regular detergents are too harsh & not only strip wool of its natural lanolin, but can also strip the color from dyed wool. After your covers are sewn, continue to use a good wool wash on the gentle cycle in warm to wash your covers once a week or when they become soiled. Lay your clean covers on a towel to air dry.
Re-Lanolizing: If you notice that your wool covers stop functioning well, it may be time to re-lanolize them. Disolve a ½ tablespoon of pure lanolin (Lansinoh® nipple ointment works great!) in a cup of hot water. Mix the dissolved lanolin into a sink or small basin of warm/lukewarm water - enough to completely cover your wool diaper cover. Allow to soak for 30 minutes to an hour. Place the cover on a towel and roll out the excess moisture and allow to air dry.