B, C, and D paper loans are types of sub-prime loans. There was a time when they were hard to find. Then when the housing market took off, so did the number of lenders offering them. Not so today. High default rates on sub-prime mortgages made to high-risk borrowers with bad credit or those who had filed for bankruptcy or had a property in foreclosure, now have many lenders either shunning these loans or tightening credit requirements on them.