Bitcoin ETFs see $433M in inflows as Ethereum ETFs add $144M in single-day surge

US spot Bitcoin ETFs pulled in $433 million in net inflows on September 18, while spot Ethereum ETFs added $144 million on the same day. Both figures represent a meaningful rebound from mixed and negative flow sessions that preceded them.

Fidelity’s FBTC was the standout performer on the Bitcoin side, attracting $311 million of the day’s total. BlackRock’s IBIT contributed $108 million. On the Ethereum front, the roles reversed: BlackRock’s ETHA led with $114 million, while Fidelity’s FETH added roughly $26 million.

The numbers behind the flows

The $433 million Bitcoin ETF inflow day arrived against a backdrop of total Bitcoin ETF assets under management reaching $102.532 billion, a figure that now represents 6.29% of Bitcoin’s entire market capitalization. Cumulative historical net inflows into these products have hit $55.161 billion since their launch.

Ethereum ETFs, while smaller in absolute terms, are growing at a pace that demands attention. Total AUM for spot Ethereum ETFs now stands at $16.719 billion, representing 5.2% of Ethereum’s market cap. Cumulative inflows have reached $13.250 billion.

The gap between 6.29% market cap penetration for Bitcoin ETFs and 5.2% for Ethereum ETFs is narrower than many expected at this stage.

Fidelity vs. BlackRock: different days, different leaders

Fidelity dominated Bitcoin flows with $311 million out of $433 million total, capturing roughly 72% of the day’s inflows into FBTC. BlackRock took a back seat with $108 million into IBIT.

Flip to Ethereum, and the script reverses completely. BlackRock’s ETHA absorbed $114 million of the $144 million total, roughly 79% of all Ethereum ETF inflows for the day. Fidelity’s FETH picked up $26 million.

What this means for the market

Bitcoin ETFs controlling 6.29% of the total market cap creates structural dynamics where every inflow day effectively removes a portion of circulating supply from the open market and parks it in cold storage under institutional custody.

With cumulative inflows of $55.161 billion for Bitcoin ETFs and $13.250 billion for Ethereum ETFs, the aggregate capital committed to these products now exceeds $68 billion.

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