From the Marmat web site:
My gear has lost some of its water repellency – What can I do?
Clean the garment. We suggest using Granger’s G-Wash Cleaner Plus.
To restore the water repellency in your gear we recommend using Granger’s Waterproofing for Synthetic Fabrics – either wash-in or spray-on versions. (You can find it in most sports specialty stores) Use the wash-in method for shell garments and follow the label directions. Be sure to use luke warm water to wash and rinse, place the garment in a drier for 45 minutes at medium heat to heat-set the fininsh and remove it promptly. For soft-shell garments, Granger’s offers Soft Shell Proof to restore water-repellency.
For more information about Granger’s garment care products, visit http://www.grangersusa.com or call Axis Outdoor at 800-335-0260 – email them at info@axisoutdoor.com.