Archival Clothing endorses waxed cotton because it’s a rugged, natural fabric that requires simple wax reproofing to maintain its finish and water repellency. Waxed cotton users should know how to reprooof their hats, bags and jackets. Both Filson and Barbour offer factory reproofing services but we recommend performing the work yourself. Reproofing waxed cotton is easy and personalizes the care and maintenance of your garment. Even if you live in the desert, you should establish a reproofing scheduled for your waxed cotton products. Reproofing extends the life of a waxed item and prevents it from developing folds and wear lines that might cause holes.
I do my reproofing work in August so I can move the work into the backyard.
Basic tools: wax (warmed), water, sponge, blow dryer (or heat gun). Some people recommend using the same paraffin wax sold by the original manufacturer. I’ve switched between several brands of wax treatment (Filson, Barbour and Martinex) with the same results. I will concede that for a full reproofing job on a jacket, the larger tins of Barbour reproofing wax are easier to heat in a double boiler.
Scrub off dirt with a moistened sponge. Do not use soaps or detergents.
Use quarter sponge to spread warmed reproofing wax. Small strokes best.
Reheat surface of fabric with blow dryer to melt down larger wax deposits.
Reapply wax until it evenly coats the bag.
Apply additional blow dryer heat treatment (direct sunlight also helps)
Returned to original factory finish 
I still have wax left so I’m reproofing a few of my Filson duckbill caps
You’ll be moving back and forth between wax applications and the blow dryer
Don’t expect the wax to glaze evenly over fabric. You’ll need to work it into surface.
Fully shellaced. Let the sun help melt the wax. Retreat with a blow dryer if you find any remaining, unmelted spots of wax. I love how stand up sturdy waxed products become after reproofing. Daily use and rain will wear down overly zealous reproofing efforts.