Cast iron.

Check out our Whitehaven collection.

http://www.us.kohler.com/us/search/searchResults.jsp?enableRedirect=true&all=true&filter-products-type=false&filter-parts-type=false&filter-techRef-type=false&filter-helpTopics-type=false&searchTerm=whitehaven&pageName=globalSearch&fromPage=search&_requestid=7242341#

I have the Whitehaven sink and LOVE LOVE LOVE it. Best purchase I've ever made.

Still hands down my favorite thing.