Portfolios are undergoing a structural transformation. Investors now have broader and more efficient access to new asset classes—from private markets to digital assets—than ever before. This shift is redefining the investment opportunity set while increasing portfolio complexity. These are among the key conclusions of “Built to Last: How Bond ETFs Are Powering a Portfolio Evolution,” a study published by BlackRock.
The firm argues that the modern asset allocation framework is no longer “a simple balance between stocks and bonds, but a multidimensional architecture encompassing public and private exposures, liquid and illiquid strategies, and both traditional and alternative sources of potential returns.”
At the same time, investors are increasingly asking what can help maintain portfolio cohesion in this more complex environment. According to the report, fixed income “can no longer be viewed solely as a counterbalance to equity risk,” as its role has evolved significantly.
“Fixed income can simultaneously meet liquidity needs, support potential income generation, facilitate disciplined rebalancing and provide a mechanism for managing portfolio volatility across changing market environments,” the report states.
Modern fixed income through ETFs
This evolution in portfolio construction is occurring alongside a transformation within fixed income markets themselves. Once viewed as opaque, dealer-driven and operationally cumbersome, the bond market is becoming increasingly digitalized, transparent and indexable.
At the center of this modernization are fixed income ETFs.
According to the study, fixed income ETFs now represent more than $3 trillion in global assets, with $669 billion in inflows during 2025 alone—exceeding the combined total inflows recorded in 2022 and 2023.
Fixed income ETFs have effectively translated the scale and breadth of the bond market into investment exposures that are tradable, transparent and operationally efficient. What began as a tactical liquidity management tool has evolved into a strategic allocation vehicle used by institutions, financial advisors and wealth investors worldwide.
The report argues that fixed income ETFs sit at the intersection of two defining trends: growing portfolio complexity and the modernization of fixed income market structure.
On one side, portfolios are increasingly incorporating more illiquid, volatile and differentiated return streams. On the other, fixed income markets have become more transparent, indexable and technologically advanced.
Bond ETFs bridge these developments by providing “the scalable liquidity, income precision and execution efficiency required to support increasingly sophisticated portfolios.” As a result, fixed income ETFs are uniquely positioned to fulfill the expanded role that bonds can play in modern portfolio construction.
A stabilizer for portfolios exposed to digital assets
Digital assets have continued to grow as more investors allocate capital to the asset class.
Cryptocurrencies, for example, have experienced rapid expansion. According to BlackRock, the total cryptocurrency market capitalization currently stands at approximately $2.4 trillion, while exchange-traded products (ETPs) providing crypto exposure have grown from $4 billion to $120 billion in assets over just three years. Today, more than 300 crypto ETPs are listed globally.
Looking ahead, the report notes that more than 75% of institutional investors expect to increase their allocations to digital assets, while 59% plan to allocate more than 5% of their assets under management to cryptocurrencies.
Over the past five years, Bitcoin has exhibited a different performance profile from bonds, with a monthly correlation of 0.21 between Bitcoin and the Global Aggregate Bond Index, compared with a 0.43 correlation between global equities and Bitcoin.
“Balancing Bitcoin allocations with bond allocations can therefore help smooth overall portfolio performance across different market environments,” the report notes.
Fixed income ETFs can also help mitigate the impact of cryptocurrency market downturns “by providing diversified exposure across duration and credit risk through a broad range of bonds, while consolidating that exposure into a single vehicle to simplify investing and facilitate efficient rebalancing.”
When portfolio allocations drift from their targets, bond ETFs allow investors to adjust exposures quickly and cost-effectively without having to buy or sell individual bonds, making portfolio rebalancing more efficient and operationally straightforward.
