Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
A seamless background texture of old cardboard.
Source V. Hartikainen
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
A seamless pattern formed from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Alternative colour scheme. 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
Continuing the geometric trend, here is one more.
Source Mike Warner
If you’re sick of the fancy 3D, grunge and noisy patterns, take a look at this flat 2D brick wall.
Source Listvetra
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
Zero CC tileable brick texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Groovy Concentric Background 2
Source GDJ
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
Not sure if this is related to the Nami you get in Google image search, but hey, it’s nice!
Source Dertig Media
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
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
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ