The riskiest types of corporate bonds are getting a makeover, providing more protection for investors while showing the limits of a rally in junk-rated debt that pushed yields to a record low.

Issuers from Neiman Marcus Group Ltd., which sold in October $600 million of notes that allow it to make interest payments in more debt instead of cash, to Jacksonville, Florida-based Bi-Lo Holdings LLC led $14.8 billion of payment-in-kind (PIK) offerings in the U.S. last year, the most since 2008, according to data compiled by Bloomberg and Fitch Ratings. The 36 issues were a record.

While the bonds became popular during the last credit boom before the downturn, the new generation of securities are smaller in size, come from companies with less leverage, and some compel borrowers to pay interest in cash unless they violate certain financial targets. These protections show that investors are treading carefully even as they search for additional yield amid unprecedented central bank stimulus measures that pushed interest rates to all-time lows.