Muc-Off Rain Shield Re-Proofer. The Rain Shield Re-proofer spray creates a cutting edge DWR (Durable Water Repellent) layer on all types of technical clothing. This simple to use spray-on waterproofing treatment is designed to restore factory levels of performance on all waterproof and breathable fabrics. It uses the latest technology to reduce the surface tension of the fabric and provide the very best waterproofing without impacting the breathability of fabrics. It also helps to protect against mud and ground-in stains.