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
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
This metal background pattern resembles a metal plate with rivets. Solid rivets on a metal plate.
Source V. Hartikainen
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
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Black brick wall pattern. Brick your site up!
Source Alex Parker
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Tiny little fibers making a soft and sweet look.
Source Badhon Ebrahim
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
A free seamless texture of reptile skin colored in a dark brown color. As always, you may use it as a repeated background image in your web design works, or for any other purposes.
Source V. Hartikainen
Prismatic Abstract Geometric Background 5
Source GDJ
Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen
Three shades of gray makes this pattern look like a small carbon fiber surface. Great readability even for small fonts.
Source Atle Mo
Prismatic Groovy Concentric Background 5
Source GDJ
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim