Municipal bonds are also relatively liquid, but investors need to be careful of the bid-ask spread. A bid-ask spread of just 1% can substantially reduce the returns of a muni bond yielding 2%. One solution is to invest in a municipal bond mutual fund, but you must be sure the fund is no load. A high load fee can be just as bad as a high bid-ask spread. Muni bond ETFs are another potential solution. However, the bid-ask spread can also be high for low-volume ETFs. The best muni ETFs usually have low bid-ask spreads.