A trend allowing creation of securities either by combining primitive and derivative securities into one composite hybrid or by separating returns on an asset into classes. Both cases are financial engineering techniques. Creative security design often calls for bundling primitive and derivative securities into one composite security. Quite often, creating a security that appears to be attractive requires unbundling of an asset.Amortgage pass-through certificate is unbundled into two classes. Class 1 receives only principal payments from the mortgage pool, whereas class 2 receives only interest payments.