Investors who want to protect themselves against rising prices have bought Treasury Inflation Protected Securities this year even though the bonds have negative yields.

So far, they haven’t needed inflation insurance. U.S. consumer prices were unchanged in July for the second straight month, the Labor Department said Wednesday.

The iShares Barclays TIPS Bond Fund (NYSEArca: TIP) has pulled back in August along with Treasury bonds as yields rise.

With TIPS, the yield is based on changes in the Consumer Price Index as well as Treasury yields. In other words, TIPS can be hurt by rising rates and deflation.

In May, the U.S. sold $13 billion of 10-year TIPS at a record negative yields.

When considering TIPS, it’s important to check the so-called inflation breakeven rate. The difference between the 10-year Treasury bond yield and the 10-year TIPS yield is “the rate at which inflation would have to be above over the next 10 years in order for an investor to be better off owning the TIPS than the Treasury bond,” explains Morningstar analyst Timothy Strauts.