I was practicing on some squares with quilting I might want to use on the finished quilt. The fabric had been prewashed as well as the backing. Used Warm and Natural batting just for practice. I put these in the washer and dryer to see what would happen. The result was a wrinkled look which I do not like, not the old fashion look, but a mess. I always use Quilters Dream Cotton, but have never washed anything with it.

Should the batting be prewashed to preserve a smoother look?

Well, not generally, unless you really want a smooth quilt. Then you might want to consider using poly batting instead of cotton, because it won't shrink at all like the cotton will.

If you want to use cotton and pre-wash, you have to wash it gently in the bathtub and hang to dry, because washer/dryer will damage it.

maybe your quilting was too far apart? I do like the old fashioned look but don't want it so drawn up that you can't see the pattern of the quilting, I wash all my fabric and I soak my batt in a tub of VERY warm water, push it down to make sure it all gets good and wet, soak for about 30 minutes and spin. DO NOT AGITATE!!!!! I ruined a queen size that way, had a piece big enough left for a small baby quilt.anyway, you get minimal shrinkage that way

Warm an natural washes up really flat unless you used fabric that was not prewashed. It is one of the things I do not like about it. I would like it to crinkle more. If you wash it on warm and line dry the quilt it doesn't really wrinkle at all but it does if you put it in the dryer and dry it till it is all the way dry. I prewash fabric and not the batting but I am experimenting with using fabric that was not prewashed and then drying in the dryer, then the batting does crinkle up more as does the fabric but teh quilt might get an odd shape look.

There are pre washing on the W & N batting if you don't want any shrinkage. I am not a fan of it (shrinkage) & use the 80/20.

I like the crinkled look so I don't prewash my batting or fabric.

I only use Quilter's Dream and it says NOT to prewash. Frankly I wouldn't wash any other batting either. I can't remember what cotton batt I used before I started with Quilter's Dream only but would never have washed it. I did throw some in the dryer on occasion if they were really wrinkled but you could also lightly press the wrinkles out if needed. I spray baste and so it is easy not to have to worry about kinks in batting as you just smooth it out as you sandwich your quilt.

unless poly batting I always wash and dry flat---ish.

I have never washed batting..throw it in the dryer and go with it