Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
Seamless Background For Websites. It has a texture similar to cork-board.
Source V. Hartikainen
A classic dark tile for a bit of vintage darkness.
Source Listvetra
Prismatic Abstract Background Design
Source GDJ
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Dark Tile-able Grunge Texture. I think this texture can be classified as grunge. It's free and seamless, as always.
Source V. Hartikainen
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
Washi (和紙?) is a type of paper made in Japan. Here’s the pattern for you!
Source Carolynne
Prismatic Geometric Pattern Background 2
Source GDJ
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. Version with black background.
Source Firkin
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
One more updated pattern. Not really carbon fiber, but it’s the most popular pattern, so I’ll give you an extra choice.
Source Atle Mo
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
Colourful background achieved with gradient fills.
Source Firkin
A background pattern with blue on white vertical stripes.
Source V. Hartikainen
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin