Sashiko thread is made of cotton, is relatively thick and matte. Unlike embroidery floss, it is spun in such a way that the threads cannot be separated; it is used as is.
This thread is thinner than traditional sashiko thread, making it more suitable for thinner materials. Sashiko is often done on denim, linen, hemp, and so on. With a thinner thread, you can more easily sew on lighter and thinner materials, or even on thick ones, for a finer line and a different effect.
The thread is from Olympus Japan, a company over 100 years old! In other words, they have a lot of experience :)
Sashiko thread is a little more "fluffy" than embroidery floss, and adheres nicely to the fabric you are sewing into, blending in over time as an integrated part of the material.
Here you get 20 colors at once, great for small repairs! The thin threads can be bought in balls of 80 meters (here), while these bundles are 10m each.
You can find sashiko needles and thimbles here :)