Oatey® No. 5 Paste Flux is a petrolatum-based flux designed to provide superior wetting properties for better solder flow. It can be used with most soft solders, 100% lead-free and safe for use on potable water applications. No. 5 Paste Flux's formula prevents copper piping turning green and is excellent for large diameter copper pipe applications. Oatey products have earned the trust of plumbing professionals for over 100 years.