State Street SPDR Nuveen ICE High Yield Municipal Bond ETF (HYMB)

HYMB is an exchange-traded fund that holds a portfolio of high-yield municipal bonds — tax-exempt debt issued by U.S. states, cities, and local authorities with below-investment-grade credit ratings — targeting investors seeking income exempt from U.S. federal (and sometimes state) income tax.

The origins of municipal bond funds

Municipal bonds emerged in the nineteenth century as a way for cities and states to finance infrastructure — canals, railroads, water systems, schools — without tapping the federal government. The tax exemption (federal and often state-level) became the great incentive: a bondholder in a high tax bracket could earn a 5 percent tax-free yield, equivalent to an 8 or 9 percent taxable yield depending on their bracket. This made munis attractive to wealthy individuals and, later, to insurance companies and banks.

As infrastructure finance grew, the municipal bond market fragmented into thousands of issuers — every state, every major city, every local authority had its own credit profile and its own track record of payments. For most of the twentieth century, munis were a hold-to-maturity asset: you bought a bond from your local government and held it for years. The market was opaque, traded over the counter, and dominated by wealthy individuals and professional bond traders. Default was rare but not unheard of; a few cities and authorities defaulted spectacularly (New York City in 1975, Stockton and Detroit in the 2000s), but most paid reliably.

The ETF revolution of the 2000s and 2010s transformed muni investing. Index funds began tracking the broad municipal bond market, making it possible for smaller investors to own a diversified portfolio of munis rather than a few individual bonds. Exchange-traded funds made it easier to trade, and passive investing brought costs down dramatically. By the 2020s, muni ETFs held significant portions of the outstanding municipal bond market.

From broad indices to high-yield niches

Early muni ETFs tracked broad indices weighted by the size of outstanding debt across all credit qualities — everything from pristine AAA-rated state general-obligation bonds to junk-rated local authority debt. HYMB represents a more recent strategic narrowing: high-yield municipal bonds specifically.

High-yield munis are debt issued by states, cities, or authorities with weaker credit profiles. A rustbelt city with shrinking tax base and high pension liabilities might issue munis rated BB or B. A special-purpose authority funding a project with uncertain revenues might issue below-investment-grade debt. These borrowers need to pay higher yields to attract investors, and the tax exemption remains their advantage: a 5 percent tax-free yield on a junk muni is still attractive to a high-income investor in a 40 percent federal-plus-state tax bracket, equivalent to an 8.3 percent taxable yield.

The strategy of specializing in high-yield munis became viable once the muni market was large and liquid enough to support it. The Nuveen indexing team, working with the Intercontinental Exchange, created an index of high-yield munis, and State Street packaged that index into an ETF under the SPDR banner. The result is HYMB.

The tax-exemption advantage and its limits

The core appeal of HYMB to any investor is simple: the interest it distributes is exempt from U.S. federal income tax. For a person in the top federal bracket (37 percent) plus state income tax (up to 13 percent in high-tax states), that exemption is worth real money. A 5 percent tax-exempt yield is worth roughly 8 percent in taxable income, depending on the state.

But the exemption has limits. High-income investors gain the most benefit, so HYMB makes the most sense for people in high tax brackets. A person in a low tax bracket gets less benefit from tax-exemption and would be better off in a taxable bond fund. Also, the exemption applies only to the income (the interest); if you sell a muni bond or a muni ETF at a profit, you owe capital-gains tax on the gain. And if you hold HYMB in a tax-deferred account like an IRA (where all distributions are tax-deferred anyway), the tax exemption provides no advantage — you might as well hold a higher-yielding taxable bond fund.

Credit risk in the muni universe

High-yield municipal bonds are credit risks. A city or county issuing junk-rated debt has real financial stress: weak tax base, high liabilities, or reliance on uncertain revenues. Unlike a junk-rated corporation, which can go through bankruptcy and emerge restructured, a municipal government has fewer restructuring options. The political economy is different — cutting pensions is politically explosive, raising taxes has limits, and defaults are rare but devastating. A few muni defaults in the past two decades have left some investors burned.

HYMB’s diversification across hundreds of muni issuers reduces single-issuer risk. If one city defaults, the fund’s loss is spread across many holdings. But the portfolio is vulnerable to systemic stress: recessions that shrink tax bases, pandemics that disrupt services, or demographic declines that depress property values. Also, different regions have different risks. Sun-Belt cities growing rapidly have stronger credit profiles than Rust-Belt cities in decline. HYMB’s index likely tilts toward larger issuers, which may include both high-growth and struggling regions.

The modern muni ETF landscape

HYMB sits in a specific niche: high-yield munis, national scope, passively managed via an index. The broader muni market has diversified into hundreds of ETFs and closed-end funds targeting different segments — intermediate munis, short-term munis, state-specific munis, investment-grade munis, insured munis. HYMB appeals to investors who want the tax-exemption advantage of municipal bonds but are willing to accept sub-investment-grade credit risk to get higher yield. It is also appealing to investors who are diversified into taxable high-yield bonds elsewhere and want a tax-efficient source of income for higher-bracket income.

How to research high-yield municipal bonds

Start with HYMB’s prospectus and recent fact sheet to understand the index composition: what percentage of the fund is rated BB or B versus CCC, what regions dominate, what types of issuers (cities, counties, special authorities, tax increments), and what the weighted-average maturity is. Compare the fund’s current yield to the yield on taxable high-yield bonds and calculate the tax-equivalent yield: if a taxable junk bond yields 6 percent and HYMB yields 4 percent, is the tax benefit worth 2 percentage points for your tax situation?

Watch credit spreads. When spreads between investment-grade and high-yield munis are wide, high-yield bonds are cheap and potentially attractive. When they’re narrow, credit risk is being compensated poorly. Read the fund’s commentary on state-level and regional credit trends: states with strong revenue growth and stable liabilities are issuing munis that are less risky than munis from distressed jurisdictions. And understand the specific risks of the issuers in the fund’s largest positions. A large pension-obligation bond issued by a poorly funded state has different dynamics than a revenue bond issued by a growing city.