4 inch anodised aluminium muffin tin. The surface can never blister or peel - even under the most adverse conditions. Anodised aluminium will never rust. Anodising effectively seals-in the aluminium, in much the same way as a non-stick coating does and gives bakeware easy-release, easy-clean properties. This pan was used with a PME basket tube to create the cake as in the thumbnail image.