You should expect many years' service from a quality waterproof shell, yet over time both dirt and general wear will begin to affect the breathability of even the best performing waterproof. They may never quite be factory fresh again, but with a bit of TLC you can easily and cheaply give tired old garments a new lease of life. Here's how: 

'Looking after your gear will save you money in the long-term' says Mike Vassar, Head of Marketing at Nikwax.

'Many people think that their waterproof jacket has had it once the water starts to soak in, but for under £10 you can keep it going for a lot longer. Cleaning and reproofing is really important from a sustainability point of view – the production of a jacket takes up a great deal of resources so making it last as long as possible is better for both your pocket and the planet.'

DWR, or durable water repellent treatment is a hydrophobic (waterproof) coating applied to the surface of fabrics to prevent them soaking up water. In most waterproof shells the DWR is used in combination with a waterproof breathable membrane, such as Gore-Tex or eVent. The idea is that the DWR prevents the outer layer from becoming saturated, allowing the membrane beneath to transport water vapour outwards as efficiently as possible. When your shell is functioning as designed, rain will bead on its surface rather than soaking in. However if the surface starts to soak up moisture, or wet out, then sweat vapour can no longer escape. The result is that you get wet and clammy on the inside even during moderate exercise.

Washing

A build-up of dirt, sweat and grease (sun screen for instance) on the outside of a shell will compromise both the DWR and the membrane, so washing a garment should always be your first move when its performance starts to tail off and it shows signs of wetting out. For the first few washes the following ought to be enough to revitalise water repellency:

• The detergents used in a standard washing powder tend to degrade the DWR, and leave behind chemical residues that attract water. So before starting make sure to thoroughly clean out the detergent drawer of your washing machine (if possible remove it entirely and wash it in the sink).
• Add the recommended amount of your chosen washing solution to the detergent compartment. Pure soap flakes used to be recommended, but they are hard to come by and most people will use a dedicated soap-based product such as Nikwax Tech Wash or Granger's Performance Wash.
• Run the machine on a cool synthetics cycle (30 degrees will do it), and a slow spin.
• Hang the garment out to drip dry.​

​Re-proofing

If washing alone has not solved the problem it's likely that the manufacturer's DWR coating has begun to degrade. It can be rejuvenated, albeit temporarily, by reproofing the garment with a dedicated wash-in solution such as Nikwax TX Direct or Granger's Clothing Repel.

• First wash the garment, as above.
• Now run the machine on a second cycle using the recommended amount of your chosen re-proofer
• Some solutions work best if you then tumble dry the garment so that the heat reactivates the DWR. Nikwax say this isn't necessary with TX Direct - the shell can just be hung up to dry.

This ad from Nikwax provides a useful summary of all the above: