The best material for a boat anchor is metal.
Metal is strong and durable, and it can withstand the harsh conditions of the marine environment. It is also heavy, which helps to keep the anchor in place.
Foam is not a good material for an anchor because it is not strong or durable. Glass is also not a good material because it is brittle and can break easily. Wood is a good material for some types of anchors, but it is not as strong or durable as metal.