The fabric and color of the kippa is usually a sign of adherence to a specific religious movement. Knit kippahs, known as ‘kippot serugot (crocheted)’, are usually worn by Religious Zionists (usually in Israel), while Modern Orthodox in American tend to wear suede or leather kippas.
Members of most Haredi (ultra-Orthodox) groups tend to wear black velvet yarmulkes or cloth yarmulkes. In general, the larger the kippa, the more ‘religious’ the wearer tends to be, though that is not as simple as it sounds. On the other hand, the smaller the kippah, the more modern and ‘liberal’ the kippa-wearer tends to be.
During the Middle Ages, the kippas Jews would wear was the ‘Jewish Hat’, which was a hat with a brim and a central point. Used originally by Jews to make themselves stand out, it was later made a requirement in some places by Christian authorities as a way of discriminating against Jews. In the United States of the 1800s, rabbis often wore a scholar's cap (similar to a beret, like a large saucer-shaped caps of cloth). Other Jews of this era wore black pillbox-shaped yarmulkes.
More recently, kippot have cartoon characters, sports teams or logos on one quarter of the kippah. Pic-A-Kippa is the first kippa company in the world to create full-image kippas, where the image is printed over the entire kippa.