The amount of loans to the riskiest U.S. companies ballooned to a record this year, propelled by unprecedented demand for floating-rate debt that offers protection from rising interest rates, Bloomberg reported. 

The market for junk-rated loans increased to $683 billion, exceeding the 2008 peak of $596 billion, according to Standard & Poor's Capital IQ Leveraged Commentary and Data.

The $130 billion surge this year was fueled by borrowings that don't include typical lender protections such as limits on leverage.

Loans, which suffered the biggest losses in the fixed-income market during the financial crisis, staged a comeback as investors funneled a record $64.4 billion into funds that buy the debt in anticipation that the Federal Reserve would start unwinding its bond buying that's suppressed borrowing costs.