An i-cord is a tubular structure that created by knitting it on a straight needle back and forth in stockinette st. Usually there are not that many stitches to knit but have to make it long. How many stitch to make depends on each instruction of the project. I-cords are used in many projects such as a string to tight a waist of a skirt, a blouse neck line to create a tie in a front or just to make a pretty decoration. I used an i-cords to make a strap for a halloween candy bag and girl shoulder bag.
When I knit an i-cord, I prefer using a pair of very short double pointed needle and I slip the first stitch at the beginning of every row.
Here is an example of how to make an i-cord video tutorial by Judy