You can use most any lightweight knit fabric to make an infinity scarf. Keep the cost down by upcycling an old skirt, blanket, sheet or even a curtain.
To make an infinity scarf, you’ll need 3/4 yard (60” wide) of lightweight knit fabric.
Fold the fabric in half the long way, pretty sides facing together inward. Pin the edges together. Stitch the long side together 1/2” from the edge by hand (remembering to backstitch) or use a sewing machine if you’ve got one.
Stick your hand through the tube you’ve just made and grab the other end. Pull it through the tube so that both rough ends meet. Line them up making sure they are even, then pin the two edges together and sew it with a 1/2” seam allowance almost all the way around. Stop sewing and leave about four inches unsewn so you can turn the infinity scarf right-side out.
Pull the scarf back through the hole that you left so it’s right-side out.
Close the hole with an invisible stitch, which you do by starting with your needle inside of the seam and pulling it straight out, then go back across and stick the needle in and down through the seam allowance. It's also known as a ladder stich. Keep going until you get to the end and tie a knot.