Summary: This is a carpet knit with t-shirt yarn and other similar cut up stretchy fabrics such as socks and tights. It is knit in seed stitch (so it lies flat) and alternates colours at least every row or so. Take care to alternate „stretchy“ with „very stretchy“ jersey yarn, so that the carpet will be nice and square. (There is a mistake in the pattern, I say moss stitch instead of seed stitch… though I’m sure the carpet would look great in moss stitch too!)

The yarn: Cut up socks (singleton socks and holey socks), cut-up old t-shirts, cut-up holey tights. The stripes are about 1 inch wide. As the colours are alternated very often, you do not need to make the stripes particular long.
Hint: Secure the yarn with bag clips when taking a break from knitting!
Edit: I made the t-shirt yarn myself, but had to choose some kind of brand yarn for the pattern as “hand-made jersey yarn” wasn’t an option to choose.

How to connect the stripes:
Snip holes in the ends of the stripes, feed Strip 1 through the hole of Strip 2. Then feed the other end of Strip 1 through the hole of Strip 1.

Warning: The cut-up yarn leaves a lot of threads on your clothing and is heavy. This is not a project that travels well or good for at work.

The knitting: Cast on about 56 stitches.
First row: sl1, k1, p1. Repeat till end of row.
Repeat first row until you reach the desired length and bind off. (One row equals about 1cm)

Color choices: I alternated every row between dark-ish and light funky colours.
Knitting needles: Size of your choice, but I used Size 12mm circular needles.
Carpet size: 115 cm lang (116 rows), 90cm breit (55 stitches), about 2 kg (4 pounds)
Disclaimer: Am terrible at counting stitches, so no size guarantees.

Finishing: I didn’t add anything at the bottom to make it skid-proof. You could sew on an anti-slip mat or use liquid rubber. It lies in front of my bed, is extremely stretchy.