A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
This is the remix of "Background pattern 115" uploaded by "Firkin".Thanks.
Source Yamachem
Prismatic Groovy Concentric Background
Source GDJ
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
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
A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
Classic vertical lines, in all its subtlety.
Source Cody L
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Have you wondered about how it feels to be buried alive? Here is the pattern for it.
Source Hendrik Lammers