Sumatra Wood is quite branchy and the pieces vary quite a bit. They are the roots of trees and are fanstastic for aquascaping. You can tie java moss onto them easily (use Aqua Fine Line) and this creates a very natural look. Some fish will graze on this wood too and shrimp will be constantly cleaning it :) Each piece will need soaking before use, otherwise it will float. Sometimes the pieces sink quickly, and other times not so quick but what I can guarantee you is that it will definitely sink over time. Try anchoring it down with rocks if you want an immediate 'sinker'.