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 seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Green Background Pattern
Source V. Hartikainen
Here's a new background image for websites with a seamless pink texture. It should look beautiful with website themes where light pink background is needed. The background is seamless, therefore it should be used as a tiled background.
Source V. Hartikainen
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Submitted by DomainsInfo – wtf, right? But hey, a free pattern.
Source DomainsInfo
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
Background Wall, Art Abstract, Star Well & CC0 texture.
Source Ractapopulous
Kaleidoscope Prismatic Abstract No Background
Source GDJ
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
A classic dark tile for a bit of vintage darkness.
Source Listvetra
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
As the original image 's page size is too large for its image size, I remixed it.
Source Yamachem
Prismatic Groovy Concentric Background 4
Source GDJ
A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.
Source Bartosz Kaszubowski
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
Inspired by a JPG that was uploaded to Pixabay by kokon_art
Source Firkin
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin