Polyester fleece is popular for outdoor wear. It is fairly resistant to dirt and stains, but light-colored fleece can get dingy. When your white fleece begins to look gray, you may think of reaching for the bleach. Don't do it. Bleach is too harsh for this soft fabric. Instead, use an oxygen-based laundry powder to whiten your dingy fleece. The dingier it is, the longer it will need to soak in a mixture of water and detergent.
Turn the garment inside out to protect the outer surface from abrasion.
Set the water temperature on your washing machine to lukewarm, and let the tub fill with water.
Stop the washing machine once it fills with water. Add an oxygen-based laundry powder, using the amount called for on the product's packaging. Use your hand to stir the water around and dissolve the laundry powder evenly.
Put your fleece garment in the washing machine along with other white garments. Allow the garments to soak for a minimum of 10 minutes before resuming the wash cycle.
Turn the washing machine back on and let it complete the wash and rinse cycles.
Remove the garment from the washing machine. Hang it up to dry, or dry it in the dryer on low heat. Check the dryer often. Most polyester fleece dries much faster than expected.