Even as sustainable investing strategies grow, financial advisors say they are cautious about adding them to their clients' portfolios.
Curtis said she offers the strategy, but does not force it on her clients, who are predominantly women. If they feel strongly about impact investing, Curtis said she will create portfolios that are 100 percent invested with sustainable funds.
"Now there's enough funds where you can build a diversified portfolio," Curtis said. "There's funds represented in every asset class now. Three years ago, there wasn't."
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But Eric Roberge, a financial planner and founder of Beyond Your Hammock, said 20 percent is the maximum allocation in these investments for his clients, who are in their 30s or 40s.
That's because there are still companies that tend to outperform that are not necessarily considered environmentally friendly, he said. Eliminating those companies could limit his clients' gains.
That could change as companies shift their strategies to become more environmentally friendly — and potentially reap stock rewards for doing so.
"At some point, the wave might shift," Roberge said. "But right now, we're not there yet. We're still very early on."
Still, Roberge said he is keeping an eye on innovation in sustainable funds. "Down the road, these types of investments are going to get better and better," he said.