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.
Kohler
millmacc
millmacc