By Tessa Berenson
February 24, 2017

This article originally appeared on Fortune

Stores can't keep enough Elmer's glue in stock because of a craft fad sweeping school-age children: making slime.

According to CNBC, sales of Elmer's glue more than doubled in December and grew overall in the second half of 2016 because of the trend. "Slime" is made with glue, water, sodium tetraborate and food coloring, and visual social media platforms like Instagram have helped boost the creation's popularity.

Now, parents around the country are showing up to stores with shelves empty of the key slime ingredient. Elmer's is making more of its glue products to meet the growing demand, and a spokeswoman even told CNBC that the company itself is getting in on the mania: Elmer's is looking into its own slime recipes to "make slime even more fun and worry-free."

This Story Originally Appeared On Fortune