Let’s talk about materials for Sashiko.
First, the fabrics. To be successful with Sashiko, it’s very important to start with right fabrics.
Traditional sashiko quilting is worked on indigo-dyed fabrics, but any evenly-woven, smooth fabric will work. Most of today’s fabrics made by machine are a lot tighter than old homespun fabrics. Since sashiko needles and threads are thicker than regular sewing needles and threads, it is harder to stitch through tightly woven fabrics.
Ideally you need to find lower thread count fabrics in cotton or linen, but some silks and wools are suitable. Denim seems to be a good choice because of the blue color, but it is so tightly woven that you will have a hard time stitching through it, so I would stay away from denim. I personally use cotton fabrics that are flat woven and a little heavier than Kona cotton.
You can bring a sashiko needle to fabric stores and try to let the needle go through the fabric before purchase to see if the fabric weave is loose enough for you to stitch.
Sashiko needles are especially made to work on Sashiko. It has a big eye to make it easy to thread, and has a sharp point to work easily on running stitches. The length of needle is your choice. As you experience the stitching, you will find out which length is comfortable for you. Traditionally, we use longer needles for stitching straight lines or large patterns, and shorter needles when working on small designs or curved designs.
Sashiko thread is a soft, twisted fine cotton thread that is heavier than quilting thread. It’s perfect for cotton, linen and wool. Although using sashiko thread is my favorite, you also can use purle cotton No. 8 and embroidery threads. Sashiko threads will spread here and there as you stitch but that is considered characteristic of this thread. I will show you how to handle sashiko thread later on.