Inspect the pillow casing for any tears or broken threads. Sew the tears and make any other repairs to the casing prior to washing so the down doesn't come out during laundering.
Place two pillows in a top-loading machine, one on each side of the center agitator post. This will ensure a balanced load, which helps eliminate bunching. Place one to two pillows in a front-loading machine, depending on the machine's capacity.
Wash the pillows in warm water on the gentle setting. Use a mild detergent. Run the pillows through the rinse cycle two or three times to ensure that all the detergent is rinsed from the down. Stop the machine before the machine reaches the spin cycle, which would promote bunching.
Squeeze the pillows over the machine or over a sink to remove as much moisture as possible. Redistribute the down evenly through the casing as you squeeze.
Machine dry on a moderate heat setting. Remove the pillows from the dryer every 20 to 30 minutes, and shake them to redistribute the down evenly through the casing. Down pillows may require two hours or more of drying time.
Cut 6-inch lengths of yarn. Ten yarn pieces are sufficient for a standard-size pillow.
Thread one length of yarn onto an embroidery needle. Pass the yarn down through the pillow, leaving a tail, then bring it back up. Tie the ends together, like you are tying a quilt. Repeat with the remaining lengths of yarn, spacing them evenly over the entire pillow.
Wash the pillows on the gentle cycle in warm water. Run them through the rinse cycle two or three times, and stop the machine before the spin cycle begins.
Machine dry the pillows until they are completely dry. Synthetic pillows typically require 60 to 90 minutes to dry completely. The yarn prevents the filling from clumping during both washing and drying.
Snip through each yarn loop with scissors after the pillows are dry. Pull the yarn from the pillows. Shake and fluff the pillows before placing them back on your bed.