The ProShares’ Bitcoin Short ETF (BITI) grew by 306% last week, firmly cementing its place as the second-largest Bitcoin ETF in the United States.

BITI now holds net short exposure equivalent to 3,811 BTC, up from just 937 BTC on June 27, according to Arcane Research. Most new inflows arrived June 29 and June 30—1684 BTC and 700 BTC, respectively.

The fund launched on June 21 and became the country’s second-largest Bitcoin ETF within just two days, trailing another ProShares investment vehicle, the Bitcoin Strategy ETF (BITO), which contains more than 32,000 in BTC, per Arcane’s data.

An ETF, or exchange traded fund, provides investors with indirect exposure to an underlying asset. This can be useful when investing in commodities or cryptocurrencies, which can be difficult to transfer or store. 

So far, the only Bitcoin ETF products approved in the U.S. are futures-based. That means they’re backed by futures contracts—cash-settled bets on what Bitcoin’s price will be at a later date—rather than current prices.

BITO was the first such product to launch in the country, making it highly popular with investors. BITI, however, is structured differently: Its performance is inversely correlated to the S&P CME Bitcoin Futures Index. In other words, investors profit when the price of Bitcoin drops.

Given that BITI is barely more than 10% of BITO’s size, that could mean ETF investors still prefer long exposure to BTC. Furthermore, Arcane explained last week that long-term exposure to BITI is actually inefficient.

A spot-based Bitcoin ETF product, backed by real Bitcoin, has continually been rejected by the Securities and Exchange Commission. The regulator is now being sued by Grayscale for its unwillingness to apply equal treatment to spot- and futures-based funds, both of which have been approved in several other countries.

Daily Debrief Newsletter

Start every day with the top news stories right now, plus original features, a podcast, videos and more.