In the past we recommended to customers to defat in XT4 bag. When the defat process was completed, the XT4 bags were cut up and placed in the IDF bag. Unfortunately, if the XT4 bag is cut into very small pieces, the sharp edges of the cut pieces can penetrate the clear polypropylene IDF bag, potentially causing leaks. We no longer recommend defatting in XT4 bags. We recommend that you refer to official methods that describes the defatting process, such as AOAC 985.29.