Somebody forgot to tell bitcoin investors that bitcoin isn't a currency.

While banks try to figure out how to profit from cryptocurrency and blockchain technology without handling digital coins themselves, and regulated derivatives exchanges begin to fuel the speculative mania by listing bitcoin futures, some bitcoiners have a different idea of what to do with their digital wealth.

Just over 50% of American bitcoin investors plan on making at least one physical purchase with bitcoin in 2018, according to a LendEDU survey conducted in November and released this week.

This sentiment may come as news to central bankers and economists who have argued that bitcoin will never become a widely used payment method, despite its mysterious creator's original intentions. Bank of France Governor Francois Villeroy de Galhau recently called bitcoin "in no way a currency, or even a cryptocurrency," but rather a "speculative asset" whose value had "no economic basis."

"I have not seen anybody provide an argument for why bitcoins are socially useful," the Nobel Prize-winning economist Joseph Stiglitz said recently.

Stiglitz appears to be ignoring several positive aspects of bitcoin, albeit ones that run counter to mainstream thinking today, as some have argued. And while most Main Street retailers still don't accept bitcoin, or any digital currency, as payment, it is possible to buy things with it. Some sellers even prefer it to cash.

Market sentiment LendEDU found surveying bitcoin investors.

Online real-estate broker Redfin lists a one-bedroom penthouse condo in Miami for which the asking price is 33 bitcoins, currently about $580,000. Redfin said the property is the first on its site for which the owner will only accept cryptocurrency, but dozens of other property owners on the site are also willing to take bitcoin as payment.

Cryptocurrency debit cards are also becoming a popular way to benefit from the appreciation of digital assets, allowing investors to spend their money much as they would a bank balance.

Even so, de Galhau isn't totally wrong. Bitcoin certainly has inspired feverish trading this year, and according to LendEDU, 77% of bitcoin investors in the United States believe the cryptocurrency will deliver even greater returns in 2018.

As a result, 74.7% of survey respondents said they plan to increase the size of their current bitcoin investment in 2018.

If bitcoin delivers on that expectation, it will be a remarkable feat. The digital currency is up nearly 1,700% from the start of this year, and was trading above $17,700 on Friday afternoon.

Despite the profit potential, 40% of respondents, a majority, said they didn't plan to sell any of their bitcoin holdings next year—evidently a sign they think bitcoin's unprecedented rise is more than a temporary bubble.

Banks are not so sure. Bloomberg reported this week that Goldman Sachs is requiring some clients to put up 100% margin on their bitcoin futures trades, due to the unpredictability of the underlying asset. On Dec. 10, CBOE Global Markets, one of the world's largest derivatives exchanges, began allowing its clients to buy and sell bitcoin futures.

When the LendEDU poll was conducted, in early to mid-November, bitcoin had not yet broken $10,000.

CME Group, the Chicago-based derivatives exchange, plans to begin listing its own bitcoin futures contract on Dec. 18.