Used basic stitch anti pilling yarn for red, yellow, and white. Used Caron simply soft for blue. This sweater is a gift for my 19 yr old son who LOVED sesame street and Ernie when he was little. He is not a sweater-wearer, nor do I trust him to care for a wool garment, so acrylic it is. :) I had a very hard time getting gauge and ended up knitting the size S to get a M. Worked out fine. Knit the whole thing in 6 days but it took me another 8 days to sew in all the ends. I knit all pieces flat and cut the yarn at each stripe because it seemed like the yarn was too thick and the stripes set too far apart to carry the yarn. Boy, did I regret this when it came time to deal with all the ends! It came out great though :). I wrapped it with a rubber duckie. LOL