On a warm June summer day, did the waterproofing.
Spend the morning in December walking in the chilly rain of December.
The parka was wet outside; the inside was dry and my shirt was dry. The parka was dryproofed in June.

The boots got wet outside. Inside the boots and the socks were dry.
My boots also got waterproofed this past June.

Good way of avoiding a cool chilly December morning. Waterproofed my winter gear in June.
DIY task with some heavy duty silicone spray from an auto department.