The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
A nice one indeed, but I have a feeling we have it already? If you spot a copy, let me know on Twitter.
Source Graphiste
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski
One more sharp little tile for you. Subtle circles this time.
Source Blunia
Some dark 45 degree angles creating a nice pattern. Huge.
Source Dark Sharp Edges
Prismatic Abstract Background Design No Black
Source GDJ
More carbon fiber for your collections. This time in white or semi-dark gray.
Source Badhon Ebrahim
Semi-light fabric pattern made out of random pixels in shades of gray.
Source Atle Mo
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
You may use it as is, or modify it as you like.
Source V. Hartikainen
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten