It tracks a high-yield municipal bond index and provides diversified exposure to U.S. municipal bonds rated below investment grade or unrated. The structure is designed to pursue tax-exempt interest income and a relatively high coupon yield at the same time.

It is well suited for medium- to high-risk bond investors who want tax-advantaged bond interest income and are willing to accept below-investment-grade credit risk.

The passively managed (index-tracking) ETF was launched by State Street (SSGA) in 2011.

The fund uses a sampling approach to track an index composed of U.S. municipal bonds rated high yield or below (or unrated). Rather than holding every constituent, it selects a subset of bonds with similar risk and return characteristics, and leverages the tax-exempt treatment of interest income to enhance effective after-tax returns.

• Tax-exempt interest income improves effective after-tax returns
• A focus on below-investment-grade munis delivers a higher coupon yield than general-purpose municipal bond ETFs

Assets under management (AUM) stand at $3.6B, with a total expense ratio of 0.35% per year.

It carries higher credit risk than investment-grade municipal bond ETFs such as MUB and VTEB, but its coupon yield is correspondingly higher. Because of the tax-exempt feature, higher-income investors benefit most from the after-tax return advantage.

As a bond ETF, it is highly sensitive to interest-rate moves and tends to come under price pressure during rate-hiking cycles. In environments where rate-cut expectations rise, both price gains and interest income can contribute to returns.

Demand from high-income investors seeking tax-advantaged bond income has supported steady inflows, though flow volatility tends to increase during periods of heightened rate uncertainty.

Tax-exempt interest income and a relatively high coupon yield are the key strengths, while high-yield credit risk and interest-rate sensitivity are the main risks.

MUB and VTEB, shown in the table, are more conservative alternatives focused on investment-grade municipal bonds — they carry lower credit risk than HYMB but also offer lower coupon yields. JMUB and CGMU take somewhat different construction approaches within the municipal bond market. CMF, which concentrates on California single-state tax-exempt bonds, can also be considered as an alternative within the muni category. For investors seeking more concentrated high-yield municipal exposure, HYD is worth a closer look.

Before investing in HYMB, investors should review the applicability of the tax benefit, their tolerance for credit risk, and the prevailing rate environment. It is important to confirm that the tax-exemption benefit is genuinely meaningful given the investor's own tax bracket.

Given the high-yield municipal focus, credit and liquidity risks interact. In rate-hiking periods, price declines and spread widening can occur at the same time, leading to elevated short-term volatility.

The fund is a suitable choice for investors who want tax-advantaged bond interest income and can accept a certain level of credit risk. For those seeking purely safe bonds, MUB and VTEB offer more conservative alternatives.