It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
Sort of reminds me of those old house wallpapers.
Source Tish
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
Alternative colour scheme for the original floral pattern.
Source Firkin
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
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 Curved Diamond Pattern 2 No Background
Source GDJ
Colour version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
A seamless background of warped stripes on paper.
Source V. Hartikainen
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
The image a seamless pattern derived from a weed which I can't identify.The original weed image is from here:https://jp.pinterest.com/pin/500744052301423641/
Source Yamachem
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Washi (和紙?) is a type of paper made in Japan. Here’s the pattern for you!
Source Carolynne
Prismatic Abstract Geometric Background 4
Source GDJ
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo