If you're one of those people who contributed to the 23 percent growth in cassette tape sales in 2018 in the United States, your next purchase may not come so easily. There's a shortage of material needed in the manufacturing of the comeback audio platform, causing delays for audio distributors.

The growth in the United States pales in comparison to the 125 percent surge in cassette tape sales last year, according to Nielsen Soundscan (and reported by Pitchfork). This still high stateside demand coupled with a shortage of high grade gamma ferric oxide is causing problems for the National Audio Company, Inc., which is the country's largest cassette tape manufacturer.

A letter that was shared by record label Hausu Mountain on Twitter outlines the underlying issue, stating that the lone factory that makes high grade gamma ferric oxide, "the magnetic material used in making professional quality audio recording tape," has been undergoing renovation throughout the majority of this year.

National Audio explained that this year they have only received two tons of the material, which is preventing them from filling orders on their typical 30-day schedule. For some perspective on those two tons, the tape manufacturing company has over 50 tons currently back-ordered, though they will be receiving 11 tons of the gamma ferric oxide in October.

Read the full letter below.

Tape sales have been climbing year-over-year in the United States, with a reported 219,000 sold in 2018, up from 178,000 the year before, which also marked a 35 percent increase from 2016. Vinyl, too, has made a massive comeback and it's on pace to outsell CDs for the first time since 1986.