DWR

Durable Water Repellancy. This is a coating applied to a fabric to make the fibers waterproof. The coating tends to lose its effectiveness with time. It can be rejuvinated with heat - washing and then drying in a warm clothes dryer or ironing the fabric does the trick. If the DWR is really old, heat will no longer be sufficient. In this case, using a DWR replacement is in order. These are liquids that are added to the washing water or sprays that are added to the wet fabric before putting it into the dryer.

Note that a DWR will not make a fabric waterproof; it makes the fibers in the fabric waterproof. It will not fill in the holes in a porous fabric.