Investors are buying up Treasurys in anticipation of a move by the Ferderal Reserve designed to lower mortgage rates and yields on corporate debt.
As a result, the average rate for 30-year fixed loans dropped to the lowest level on records dating back to 1971. It's down from 4.27% the previous week.
Rates have mostly fallen since spring as investors shifted money into the safety of Treasurys. That demand lowers their yields, which mortgage rates tend to track.