Invisible seam produced by mattress stitch.

Would you like to know how to do a mattress stitch seam in knitting? This is a step by step guide to joining two stockinette knitted pieces together with the invisible seam method: mattress stitch.

Mattress stitch is the best seaming technique for doing a vertical seam on two pieces of knitted fabric.

Note, I am using a contrasting colour but you will want to use the same or similar colour yarn to do the seaming.

Step 1: Preparing to mattress stitch

Thread your needle with the cast on tail or a length of yarn. You will want the yarn you use to seam with to be about twice the length of the seam.

Lay the two pieces you are seaming next to each other with the right sides of the fabric facing outwards.

Identify the first column of stitches on both sides of your fabric.

Mattress stitch seam preparation on stockinette stitch knitted fabric

We are going to be working with the horizontal bars in between the stitches seen below when you stretch the fabric out.

Mattress stitch seam preparation - working on the horizontal bars shown between stitches

Step 2: Start seaming

Go underneath the first bar on one of the sides you are seaming (you can start stitching the seam on the right or left side) and pull through your yarn. Leave a tail of 15cm / 6in to weave into your fabric later if you aren’t using the cast on tail.

First step of mattress stitch - threading needle through first bar between two stitches.

Step 3: Join the two pieces of fabric

Repeat the same on the opposite side by going under the first bar and pulling through your yarn.

Joining two knitted edges together with mattress stitch by going under bars between stitches.

Step 4: Repeat the alternating stitching

Repeat steps 2 and 3 by going under the next bar on the side you started your seam and then going under the next corresponding bar on the opposite side.

Continuing mattress stitch seam by threading second bar between knitted stitches.
Continuing mattress stitch seam by going through second bar between stitches on the opposite side.

Step 5: Tighten seam after every few stitches

Once you have stitched under the bars of a few rows, pull on your working yarn to close the seam. Don’t pull too tight to avoid getting a distorted seam.

Repeated stitching between two stockinette stitch knits to form mattress stitch. Before closing.
Seam after closing by pulling on yarn.
The seam appears invisible on the right side of the fabric:

On the wrong side of the fabric you will get a seam showing:

Wrong side of fabric showing seam.