A notable private equity investor said Wednesday that the boom in special purpose acquisition companies was not just a passing fad.

Apollo Global Management co-founder Joshua Harris said at the Delivering Alpha conference presented by CNBC and Institutional Investor that SPACs were filling a needed role for companies that were closing in on going public. Apollo has both raised its own SPACs and exited its position in companies through the blank check vehicles, Harris said.

“The SPAC part of the IPO market is a part of the market that’s here to stay,” Harris told CNBC’s Leslie Picker.

There has been a rush of SPACs in recent months, outpacing traditional IPOs in money raised in July and August, according to Refinitiv. The companies have raised more than $ 30 billion so far this year. Harris estimated that SPACs have gone from 3% of the market to 20% during the recent surge. 

The investment vehicles work by going public through their own IPOs, then using their cash to do a reverse merger with a private firm. The publicly traded shares of the SPAC then become the shares of the formerly private company.

Harris said that there is a desire for a quicker process to go public than traditional IPOs and an opportunity for established investment firms like Apollo to make a company more valuable by partnering with them.

“There’s a real need for quick, confidential capital and price certainty and for sponsorship in the markets. And most of the SPACs that have been done have been more emerging growth SPACs, less cash flow more growth. And what we see is the opportunity for sponsorship,” Harris said. 

The private equity veteran said SPACs are filling a funding need for companies that are ready to go public but want to speed up the process or might be hard for investors to understand. 

“We don’t have a pocket for that right now. That just goes nowhere. So SPACs provide a real pocket for pre-IPO into IPO capital that we don’t have otherwise, and we think we also could add value to the market,” he said.  

Earlier in September, Apollo filed for an IPO for its new SPAC, Apollo Strategic Growth Capital. An amended filing last week showed that the offering was looking to raise more than $ 860 million. 

Apollo is not opposed to the traditional IPO process either, and Rackspace, one of its portfolio companies, took that route in August. Harris said that one time when SPACs make more sense is when existing investors are looking for “more of a cash exit. A lot of times the IPO market doesn’t want any monetization.”