Government Bond Yields: MBB.F tracks the performance of the US Mortgage-Backed Securities (MBS) market, which is heavily influenced by US government bond yields. Higher yields typically lead to lower MBS prices and subsequently a lower MBB.F price.

Interest Rate Changes: Federal Reserve interest rate policy directly impacts mortgage rates and MBS valuations. Rate hikes can decrease the attractiveness of existing MBS, lowering MBB.F's value.

Mortgage Refinancing Activity: When interest rates fall, refinancing increases, shortening the duration of MBS and potentially decreasing their value and MBB.F's price.

Credit Risk and Defaults: While MBB.F holds primarily agency-backed MBS with low credit risk, significant economic downturns affecting mortgage defaults can still impact its price negatively.

Inflation Expectations: Rising inflation expectations tend to push interest rates higher, negatively affecting MBS values and therefore the MBB.F price.

Supply and Demand: The overall supply and demand for MBS in the market influences MBB.F. Increased supply of MBS can depress prices, while higher demand supports them.