The Korok Fabric is a key item from Tears of the Kingdom.
Tears of the Kingdom
"Tough fabric bearing a Korok design. It looks like it could be used to make a paraglider."
After the Phantom Ganon at the bottom of the Deku Tree Chasm is defeated and Korok Forest returns to normal, Oaki looks to finish his "secret room" in the Great Deku Tree's mouth. If Link gives him the four Blue Nightshades and two Giant Brightbloom Seeds he needs, Oaki gives him the Korok Fabric as thanks.