The promise of sustainable investing is straightforward: you can grow your money while keeping it out of the companies whose activities trouble you. The practice is harder. Any list of “ethical” funds will show very different approaches, conflicting ratings, and marketing that does not always match the actual holdings. The good news is that there is a repeatable process. If you work through the steps in order — decide how you want to screen, pick funds with real exclusions, understand the ratings, check for greenwashing, and start from a cheap core — you can build a sustainable portfolio that costs little more than a plain one and genuinely reflects your values.
Step 1: Choose your screening approach
Before you can pick any fund, you need to decide what “sustainable” means to you, because that single decision shapes everything downstream. There are broadly five ways to build an ESG portfolio, each with different strengths and weaknesses:
| Approach | How it works | Strengths | Weaknesses |
|---|---|---|---|
| Exclusion (negative screening) | Removes tobacco, weapons, fossil fuels | Simple, cheap | Limited influence |
| Integration | ESG scores folded into stock selection | Broad diversification | Scores vary by agency |
| Best-in-class | Top ESG scorers in each sector | Diversified | Still holds oil majors |
| Thematic | Clean energy, water, circular economy | Conviction exposure | Concentrated, volatile |
| Impact | Funds measurable outcomes (green bonds) | Real-world change | Smaller, less liquid |
Exclusion is the bluntest and cheapest method, simply removing the industries you object to. Integration folds ESG scores into normal stock selection, keeping broad diversification. Best-in-class buys the top ESG scorers within each sector — which keeps you diversified but still means holding oil majors. Thematic funds concentrate into one area like clean energy, offering conviction but more volatility. Impact funds aim at measurable real-world outcomes, typically through green bonds, but the universe is smaller and less liquid.
The sensible structure is a core of exclusion and integration funds (roughly 80-90% of the portfolio) doing the heavy lifting, with thematic funds treated as a satellite at the edges.
Step 2: Choose the right ESG fund
Once you know your approach, evaluating any individual fund comes down to five questions. The first is what it benchmarks against — a genuinely ESG-screened index such as the MSCI World SRI or the FTSE All-World Choice, not just a plain index that has been relabelled. The second is what it actually excludes; read the exclusion list, because the fund name alone tells you almost nothing. The third is tracking error — how far the fund is allowed to deviate from its parent index, which tells you how aggressively it is screening. The fourth is cost, because screening is not free and a reasonable TER for an ESG ETF is roughly 0.15-0.25%. The fifth is track record: give a fund at least three years so you can see how its screens behaved during an actual downturn.
Step 3: Understand ESG ratings
Sooner or later you will compare two ESG funds and run into the ratings problem. Three agencies dominate the market, and they disagree as often as they agree:
| Agency | Scale | Direction | What it measures |
|---|---|---|---|
| MSCI | AAA to CCC | Higher is better | Industry-relative ESG score |
| Sustainalytics | 0 to 100 | Lower is better | Exposure to material ESG risks |
| S&P Global | 0 to 100 | Higher is better | Corporate sustainability assessment |
The trap is thinking these scores can be compared directly. They cannot. MSCI gives a relative score within an industry, so a company can be the best in a bad sector and receive a high AA; Sustainalytics measures absolute exposure to material ESG risks, so that same company might rank “High Risk.” A firm can legitimately be MSCI AA and Sustainalytics High Risk at the same time. The rules are simple: never compare a MSCI score to a Sustainalytics one, and only use ratings to compare funds within the same agency.
Step 4: Check for greenwashing
The single most important habit in sustainable investing is to treat a fund’s marketing page with suspicion and look at its holdings instead. A few telltale signs separate genuine screening from a rebranding exercise. A real ESG fund publishes its full holdings list and puts its exclusion list in the prospectus; it screens against a defined benchmark index and discloses its engagement and voting policy; and its fees are in line with its peers. The red flags are the opposite: “ESG” in the name but fossil fuels in the top ten, only a vague “ESG tilt” with no stated screens, an attempt to track a plain index while calling it ESG, no engagement policy, and premium fees that buy no extra screening.
It is also worth remembering the case of best-in-class funds, which can hold energy majors because those firms score top of their own sector. That is defensible in the sense that the screens are doing their job — but it can be a genuine shock if you assumed “sustainable” meant “no oil.” It simply has to be the thing you intended to buy.
Step 5: A sample five-fund sustainable portfolio
To make this concrete, here is a realistic, low-cost blend that brings the principles together. None of this is a recommendation — it is an illustration of how a cheap core plus a thematic satellite might actually look:
| # | Fund (ticker) | Focus | TER | Allocation |
|---|---|---|---|---|
| 1 | Vanguard ESG Global All Cap (V3AA) | Global equities incl. small caps, ex-controversial | 0.24% | 40% |
| 2 | iShares MSCI World SRI (SUSW) | Developed world, strict SRI screen | 0.20% | 20% |
| 3 | Xtrackers MSCI World ESG (XDWD) | Developed world, benchmark-style ESG | 0.19% | 15% |
| 4 | Vanguard ESG US Stock (ESGV) | US large/mid cap ESG | 0.09% | 15% |
| 5 | iShares Global Clean Energy (INRG) | Thematic satellite (wind, solar) | 0.65% | 10% |
The resulting weighted TER is roughly 0.26% — barely above a plain index portfolio. The three global funds are doing different jobs: V3AA adds small-cap breadth, SUSW tightens the screen with a strict SRI filter, and XDWD keeps tracking error low relative to the parent index. ESGV concentrates the US large-cap part of the market, while INRG is the thematic satellite, carrying most of the volatility. The discipline is to rebalance back to these weights each year, ideally inside an ISA or SIPP so the gains stay free of capital gains tax and the income is sheltered.
Step 6: Annual review checklist
A sustainable portfolio is not set-and-forget. Once a year, run through a short list of checks. Confirm the holdings still match the fund’s mandate, because screens drift as the underlying indices change. Look for any new controversies among your top holdings, since ratings can lag reality. Confirm the TER has not crept up, because fee increases compound quietly. Check whether the thematic satellite has grown past its 10% target and rebalance it back. And — the one metric no rating agency measures — ask yourself whether the portfolio still reflects your values, because those can change as much as any index.
Bottom line
Building a sustainable portfolio is a six-step discipline. Choose a screening approach and build your core from exclusion and integration funds. Select funds by what they actually exclude, not by their names. Understand that ratings from different agencies are not interchangeable. Run a greenwashing check on every holdings list. Start from a low-cost ESG core like V3AA, and review it annually. Done this way, an ESG portfolio costs little more than a plain one and reflects your values in the way that actually matters — through the companies it holds, not the label on the tin. Remember, this is educational guidance rather than financial advice; always check the current fees, holdings and tax rules for your own situation before acting.