Can I use an aftermarket product to make a dry bag waterproof again?

A dry bag is made of a fabric which has some kind of waterproof barrier attached. The waterproof barrier may be:

• a coating on the inside (Ultra-Sil Dry Bags, Lightweight Dry Bags)
• a film laminated to the inside (Big River Dry Bags)
• a membrane sandwiched between an inner and outer layer (the base of Evac Dry Bags)
• a film laminated to the outside and inside (Hydraulic Pro Duffle)

If the coating, film or membrane become damaged or degraded (see below), the dry bag will no longer be waterproof.

An aftermarket treatment (like Nikwax TX Direct or Grangers Repel Plus) will not make a previously waterproof fabric waterproof again if the coating, film or membrane have become compromised.

These aftermarket treatments are designed to refresh or enhance the durable water repellent (DWR) finish that helps water droplets bead up and run off of the outside of the fabric. In this regard, they will improve the water repellency of the fabric, but they will not restore the ability of a fabric able to support water pressure.

What can degrade coatings, films and membranes?

• Physical abrasion can wear away a coating or a film. A very lightweight coating can be damaged by the fine grain sand suspended in water (which is one of the reasons why we specify that Ultra-Sil Dry Bags are not suitable for boating use)
• Hydrolysis can soften coatings and films and leave them porous. This particularly affects very lightweight coatings and films (and is the reason we recommend storing outdoor gear in a well-ventilated space)
• Solvents can damage coatings, films and membranes or cause them to delaminate. Solvents common in the outdoors are DEET (in mosquito repellent) and gasoline/petrol (used in some stoves)
• Oil can compromise coatings and membranes so they 'siphon' water. Oil in the outdoors comes in the form of lubricants and also in sunscreen.
• Detergent Residue can compromise lightweight coatings and membranes so they 'siphon' water. If you wash outdoor gear with store-bought detergents, make sure to rinse it really thoroughly. Washes like Nikwax Tech Wash or Grangers performance wash are preferable