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 seamlessly tile-able grunge background image.
Source V. Hartikainen
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Remixed from an image on Pixabay, the original having been uploaded by darkmoon1968.
Source Firkin
Someone was asking about how to achieve a fur pattern at #inkscape irc so tried to make a filter on it. Flood filled fractal noises rigged together. May someone find a good use for these.
Source Lazur URH
A seamless texture of black leather. I think it will look best when used in headers, footers or sidebars.
Source V. Hartikainen
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
From a drawing in 'Jardyne's Wife', Charles Wills, 1891.
Source Firkin
You may use it as is, or modify it as you like.
Source V. Hartikainen
Abstract Ellipses Background Grayscale
Source GDJ
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
Beautiful dark noise pattern with some dust and grunge.
Source Vincent Klaiber
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Here is a new seamless wood texture for using as blog or website backgrounds.
Source V. Hartikainen
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
The image a seamless pattern of a wire-mesh fence.I want you to use this pattern as a lower layer.
Source Yamachem
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Prismatic Groovy Concentric Background
Source GDJ
A beautiful dark padded pattern, like an old classic sofa.
Source Chris Baldie