By doing an Overfill, we add additional down throughout your sleeping bag. This increases the warmth of the bag by around 5 degrees. Overfills also improve loft duration. During extended use down becomes clumped with moisture, dirt, and oils. An overfill prevents this by adding more fluff. Check out this list of over-fillable items and the cost:

To specify your overfill please ensure that you have the proper bag and then select the overfill.  If you have questions please contact us prior to ordering.