I was given Warm and Natural that would shrink, and I don't particularly like the shrunken look.
It is quite easy on a top loading machine. Put the batting into the washing machine and fill it (I always use hot water). DO NOT allow to aggitate. Just let it sit for 15 to 20 minutes and then spin the water out. Put the batting into the dryer and dry it. I used hot or warm to dry it. I was trying to shink it so hot is just fine. When it is dry take it out and it's ready to go. The only thing you need to do when drying is perhaps clean the lint trap a couple of times.
I have not been as fortunate with the front loading machines, but they work too. They seem to work okay if I wash them on delicate and then dry in the machine, but they are pretty wet when they come out of the washer and take a long time to dry.
You can also fill your bathtub with hot water, submerse the batting and let sit for awhile. Drain the tub and roll up your pants and pretend you are stomping grapes. It actually sounds like it would be a pain, but it works quite well. Get it as stomped out as you can, get it into a carrying container and into the dryer it goes.
I have never tried it, but have been told that if you lay the batting out and spray water onto it (with a hand sprayer that you would use to wet your hair or whatever) just so it gets good and damp and then dry it that it also will cause it to shrink.
Seems to me that it is the heat from the dryer that causes the shrinkage.
I hope that the above methods and information will help.
amh