One of the great benefits of sustainable investing is that it’s largely about your interests – your priorities, your impact, your long-term goals. Sustainable investments put your personal values at the center of your financial planning, where they belong.

But is sustainable investing a strategy for your entire portfolio? Or is it better viewed as an add-on?

This question resonates throughout the sustainable investing community. Some view sustainability and governance data as an information advantage that should be applied to all of your investments. Others are focused on taking advantage of specific opportunities, like alternative energy or women-led businesses.

But thoughtful investors and advisors I talk to don’t necessarily think there’s a right or wrong answer. So this week’s Aha Moment gets to the heart of building a sustainable portfolio: Do you want to think horizontally, or vertically?

Vertical vs horizontal

This “vertical vs horizontal” language comes from Janine Firpo, cofounder of Invest for Better, a nonprofit that builds communities of women investors and has helped many women get started investing their values.

“I think about broad market funds as horizontals, and about targeted funds as verticals,” says Firpo. Funds and ETFs that fit the broad market profile will generally have large portfolios of well-known companies, diversified across many different sectors, that prioritize financial data but apply an additional layer of analysis related to sustainability and corporate governance.

Targeted funds and ETFs focus more intently on one specific issue or theme, such as alternative energy, affordable housing, or animal welfare.

Horizontal = Core

When you’re trying to plan for your long-term financial goals, building a portfolio around a few horizontal-type funds or ETFs offers a lot of advantages. These core investments typically prefer established companies with good track records, are benchmarked against familiar indexes and are managed to pursue a good return compared to the level of risk involved.

Most of your larger fund providers, and a handful of sustainability specialists, offer horizontal-type offerings, and some of them are extremely popular. The iShares ESG Aware MSCI USA ETF ESGU , for example, is an index fund that tries to match or exceed broad market performance using MSCI ESG data.

The Parnassus Core Equity Fund is one of the largest actively-managed sustainability funds, with about $30 billion in assets and a track record going back to 1992.

Not all of these core investments use the same data or the same strategy, and they vary a lot in terms of performance and expense ratio. So it’s important to vet them as you would any investment. But if you’re looking for a sustainable investment to use as a centerpiece in your financial plan, horizontal-type funds are a good place to start.

Vertical = Targeted

Where horizontal funds are more about broad goals and diversified investments, vertical funds hit hard on one specific goal or theme. There are hundreds of these targeted funds, and they represent a huge number of options. Many of them are ETFs; some are traditional mutual funds. Performance, risk, and expenses range widely.

Many of them have broad portfolios that apply a sustainability concept to numerous sectors, such as the TCW Transform 500 ETF NETZ – a diversified portfolio of established companies that have highly ranked employment practices. Others are like Invesco Solar ETF TAN – concentrated portfolios that reflect a well-defined theme.

Vertical-type funds should play a different role in your portfolio.

“Targeted funds are popular with sustainable investors because they provide an opportunity to have a lot more impact,” says Firpo. “Over the long-term, the vertical funds might outperform your horizontal holdings. But, in most cases, they’re going to be more volatile because they hold fewer stocks and have a narrower sector focus.”

Building a sustainable strategy

Firpo is in favor of an approach where you put the majority of your money into horizontal plays, but then “season” your portfolio with vertical plays that are strongly aligned with your specific values. A good rule of thumb is for that seasoning to represent about 5-10% of your total assets.

Of course, any time you’re talking about building a portfolio, there’s going to be other factors involved – your financial goals, risk tolerance, tax situation and others. Financial advisors can be allies on this journey, though you’ll need to make sure your advisor is comfortable with and knowledgeable about sustainable approaches.

If you’re not sold on getting an advisor, there are a lot of resources available so you don’t have to go it alone. For example, Equities.com’s Fund Finder tool can help you find vetted funds that would fit the horizontal and vertical categories.

But Firpo argues that what tends to help sustainable investors most is to talk to other sustainable investors. This is particularly true for women, who tend to underestimate their investing skills.

“We built Invest for Better to provide women with a safe, supportive space to talk about their money, investing, and the way they can use their assets to grow their wealth and build a better world at the same time.”

We often think of investing as a solo endeavor, so it’s an appealing Aha Moment to discover that you can talk it out with a community of people who are in your shoes – whether you are investing horizontally, vertically or in any other way.

More of The Aha Moment: 3 lessons from ‘oldheads,’ sustainable funds born before that was a thing