The Warm Company recommends these steps if you want to pre-wash their polyester batting (Soft and Bright):
Pre-Wash & Care Instructions
Hand Wash with mild detergent. Do not agitate or spin in washer.
Soak for 20 minutes, rinse several times.
Squeeze out water. DO NOT WRING. Rolling in a towel helps.
Dry in a warm dryer or lay flat to air dry.