While there can be several different tranches in structured finance products, Casten's default implementation is a common two-tiered structure, with two different tranches. In finance, this is usually called an A/B tranche or junior/senior tranche structure. In this case, the first class of shares (A/Senior class) usually has a rather stable but lower return than the second class (B/Junior class). In exchange, the junior class usually has higher, but also more variable returns, as it protects the senior class from losses (e.g. from defaulted assets).