I'm re-waterproofing my gore-tex jacket with Grangers Performance Repel Plus DWR. The instructions on the bottle say that after washing and applying DWR you can either drip-dry the jacket or put it in the tumble drier at 40deg. The instructional video on the Arc'teryx website says to tumble dry and doesn't mention drip drying.
Does tumble drying improve the efficacy of the DWR coating, over drip drying, or are they just recommending it because American and assume that everyone's going to tumble dry everything?
Edit: found the answer on the Gore-Tex website:
Restoring your factory applied DWR is easy, simply wash and apply heat. To restore the water repellency of GORE-TEX outerwear, GORE-TEX brand recommends the following steps:
Machine wash your garment as described in the wash instructions. Line dry your garment or tumble dry it on a warm, gentle cycle.
Once it is dry, tumble dry your garment for 20 minutes to reactivate the durable water-repellent (DWR) treatment on the outer fabric.
If unable to tumble dry, iron the dry garment on the gentle setting (warm, no steam) by placing a towel or cloth between the garment and the iron. This will help reactivate the DWR treatment on your garment’s outer fabric.
These steps will restore the factory durable water repellent treatment and water may bead up on your outerwear. If it does not, it’s probably time to apply new DWR to your jacket.