A free background image with a seamless texture of cardboard. This texture of cardboard looks quite realistic, especially when is actually tiled.
Source V. Hartikainen
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
From a drawing in 'Royal Ramsgate', James Simson, 1897.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Retro Circles Background 5 No Black
Source GDJ
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
A bit of scratched up grayness. Always good.
Source Dmitry
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
Colorful Floral Background 3 No Black
Source GDJ
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Light gray paper pattern with small traces of fiber and some dust.
Source Atle Mo
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo