haven’t had to replenish it on my Aero yet, but have done so on my GoLite Wisp. I used the wash in (despite some questions i’ve asked on this website about the possible “cons” of doing so). Figured that it would get better “coverage” with the wash in vs. me missing a few spots with the Spray-on. Wash-in worked very well. I used about 2x as much as what the said (i don’t recommend that you do that – i’m just saying that i did that). my Wisp seems now to be MORE water resistant than when new. Had it out twice in rains that should have wet it through – once mod-heavy with large drops; ~1/2mile walk to the car (i walk ~3mph – slower on the trail) – water just beaded up on it and rolled off.
I dried mine on low heat so as not to damage the fabric. if you’re going to use hi heat (unless the label/care instruction say Do Not use hi heat – then of course don’t use hi heat), check it every 5minutes and remove it as soon as it is dry.
oh…BTW…after the washer fills and begins agitating – make sure to turn off the water (assuming you have a shut-off valve), so that when the Washer’s Timer moves onto the Rinse cycle, no water enters the machine – this would remove/rinse-out the DWR before it is “heat set” by the dryer. After ~20minutes of washing, you can place the Washer into the spin mode to remove any extra water before placing it in the dryer.
hope this info helps. was the explanation clear?