Hemp and marijuana are different types of cannabis plants. Unlike marijuana, hemp produces very little tetrahydrocannabinolic acid (THCA, which turns into THC when heated). THCA/THC is responsible for producing the psychoactive effects of marijuana.
Hemp production began waning in the U.S. around 1937, when the Marijuana Tax Act instituted strict regulations on the cultivation and sale of all cannabis, including hemp. The Controlled Substances Act of 1970 took that a step further, classifying all forms of cannabis as Schedule I drugs. That made it illegal to grow hemp in the United States. Since then, U.S. manufacturers have only been permitted to import hemp from countries in the European Union and Canada.
But hemp has recently had a bit of a renaissance in the U.S. In 2014, the U.S. Farm Bill permitted states to pass their own industrial hemp legislation for research and development purposes. States like Kentucky, Colorado and Oregon are already conducting their own hemp pilot programs, and other states are pushing to enact similar legislation.
As interest in industrial hemp has grown, so too has interest in hemp-centric production. Hemp building and construction materials have been picking up real steam among advocates who say they represent environmentally friendly and sustainable alternatives to traditional building materials like concrete.