Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
A seamless pattern formed from cross 4. To get the original tile select the rectangle in Inkscape and use 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
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Light gray paper pattern with small traces of fiber and some dust.
Source Atle Mo
I’m starting to think I have a concrete wall fetish.
Source Atle Mo
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
A free seamless background texture that looks like a brown stone wall.
Source V. Hartikainen
Number 5 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Bright Multicolored Floral Background by Karen Arnold from PDP.
Source GDJ
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A very dark spotted twinkle pattern for your twinkle needs.
Source Badhon Ebrahim
Prismatic Basic Pattern 2 No Background
Source GDJ