Slub is the thickening that occurs along a spun yarn where the fibre bunches, and a cloth woven with plenty of it will never sit flat. That is the case here: a canvas with genuine depth to its surface, rustic in the proper sense of the word rather than the decorative one, the irregularity being in the thread and not applied afterwards.
Formafantasma designed it. A textile face on a nonwoven ground, sold by the metre at 130 cm wide, in four colourways. Certified to EN 13501-1, ASTM E-84 and IMO 5, and tested to EN 12149. Made in Italy.
