Batting

How do you pre-wash batting, specifically, Bamboo?  Also, do you put it in the dryer or line dry?

I'm still a newbie to sewing, so I'm not any help.. but that's a good question, I hope you get an answer soon.

Doesn't it say on the package? If it doesn't, email the company. They might tell you that you don't need to prewash it. If they do, ask for the shrinkage percentage and decide if that is acceptable to you.

I bought my cotton/bamboo batting at JoAnn's fabric store a few months ago.  I just finished 4 hours of basting the batting into my son's quilt and am not sure what to do next.  Though my fabrics are very soft, the sandwiched quilt feels as if sand or grits (if you know what that is) has been sprinkled between the layers.

I may take it by JoAnn's to see if they think this is the way it should feel.  Any ideas?

is there anyway you can make a tester/sample of what you are doing with that batting adn then washing it to see if that feeling goes away?

My friends who knit with bamboo yarn say it is rough at first but gets softer with each washing.

I machine washed and dried my bamboo batting, but it's very thin.  I think the package directions were to handwash and to dry flat, but I have a front loader and used the air dry setting.  It seemed to turn out fine. 
Bamboo is a little harder to work with than the warm & natural which I prefer.  It does feel rough, but as the others wrote, it softens up with use.  I still don't know if I would buy it again just because I still don't trust it enough... yet. 
 

Unless you are going for a vintage-y look where there is puckering from the fabric and/or batting shrinking, you'll want to wash your fabric & batting the same way you plan to wash the item when it's finished. 
I've been pretty happy with the bamboo batting, in fact, I like the tackiness that it gives when I'm basting.  I think it has a bit of an odor, but that seems to dissipate.
I usually fill the washer up with warm water & swish the batting around a bit by hand, then switch it over to the spin cycle.  I have a rack in my dryer, so I fold the batting up & put it on the rack.  Every 15 minutes or so, I refold the batting, so the damper parts arefacing out.  When it's close to being dry, I'll take the rack out & give it a few minutes on the touch-up setting.