Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
This is the remix of "plant pattern 02".I changed the object color to white and the BG to purple.The image a seamless pattern derived from a weed which I can't identify.The original weed image is from here:jp.pinterest.com/pin/500744052301423641/
Source Yamachem
Can’t believe we don’t have this in the collection already! Slick woven pattern with crisp details.
Source Max Rudberg
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Looks like an old rug or a computer chip.
Source Patutin Sergey
Tiny, tiny 3D cubes. Reminds me of the good old pattern from k10k.
Source Etienne Rallion
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A seamless texture of worn out "cardboard".
Source V. Hartikainen
A pattern formed from repeated instances of corner decoration 8. To get the basic tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
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