The financial institutions that originate the loans sell a pool of cashflow-producing assets to a specially created third party that is called a Special-Purpose Vehicle (SPV). The SPV is designed to insulate investors from the credit risk of the originating financial institution. The SPV then sells the pooled loans to a trust, which issues interest bearing securities that can achieve a credit rating separate from the financial institution that originates the loan. The typically higher credit rating is given because the securities that are used to fund the securitization rely solely on the cash flow created by the assets and not on the payment promise of the issuer. Monthly payments from the underlying assets - loans or receivables - typically consist of principal and interest, with principal being scheduled or unscheduled. The cash flows produced by the underlying assets can be allocated to investors in different ways. Cash flows can be directly passed through to investors after administrative fees are subtracted, thus creating a "passthrough" security; alternatively, cash flows can be carved up according to specified rules and market demand, thus creating "structured securities."