For many folks that are well into retirement, conventional wisdom has been that the bulk of their fixed income portfolios belong in U.S. Treasuries due to perceived safety. That perceived safety increases the allure of an ETF such as the iShares Barclays 20+ Year Treasury Bond Fund (NYSE: TLT ). The iShares Barclays Treasury Inflation Protected Securities Bond Fund (NYSE: TIP ) is another popular option for the same reasons.