As more investors consider diversifying with socially responsible investment strategies, many often find that they lack a clear gauge to assess sustainability metrics.

According to Morningstar data, investors added $51.1 billion of net new money into environmental, social, and governance (ESG) assets in 2020, setting records for the fifth year in a row, CNBC reports.

As the momentum behind ESG investments picks up, certified financial planner Phuong Luong, principal financial planner at Saltbox Financial, warned that there aren’t clear definitions of values-driven assets, which may confuse investors.

While there are broad definitions for sustainable investing that use ESG criteria through the investment process, experts have argued that there are clear distinctions within the space.

For example, socially responsible investing, or SRI, started with excluding certain sectors or industries from portfolios, like tobacco or weapons, in order to better-align with an investor’s values or beliefs.

The increasingly popular ESG theme is also a values-based strategy, but these types of funds can be more returns-focused, with broader criteria for portfolio assets.

Rachel Robasciotti, founder and CEO of Adasina Social Capital in San Francisco, also added that impact investing focuses more on the direct and specific effects of the assets.

“It’s not just about what you say,” Robasciotti told CNBC. “The metrics are about what you do.”

Due to these varying definitions in the space, investors who are interested in values-driven investing may struggle to measure their portfolio’s impact.

“To me, the biggest and most important thing to look at is who decided that metric,” Robasciotti said.

Luong also argued that limited public information may also be impeding screening for values-driven funds. For example, while names like “social” or “green” could signal that the fund manager considers these factors, investors may not have access to the underlying criteria or data used to make the investment decisions.

“Traditional ESG data typically is proprietary, meaning behind a paywall,” Luong told CNBC.

For more news, information, and strategy, visit the ESG Channel.