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
Prismatic Abstract Geometric Background 4
Source GDJ
This was formed by distorting an image of a background on Pixabay.
Source Firkin
The base gradient edited so now more details are rendered.
Source Lazur URH
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
This was formed by distorting an image of a background on Pixabay.
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
A frame using leaves from an image that was uploaded to Pixabay by mayapujiati
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857
Source Firkin
Original minus the background
Source Firkin
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin