Sealing supply pipe

When I was earlier replacing my PVB I fiddled with the copper supply pipe coming out of the house. The installers had some sort of soft white material to seal between it and the siding. It's not a caulk;can someone tell me this stuff is? Thanks

Most people use: Electrical Conduit Seal which lasts some 15-20 years or more. It is like chewing gum:

http://www.acehardware.com/product/index.jsp?productId=1292747&CAWELAID=109328419

Inexpensive, easy to apply.

HTH

Thumb Gum....