In addition to the semi-rigid soles, Spenco also sells semi-flexible soles. Based on product descriptions however, it was not clear what, if any, difference there is between the two (apart from a variation in colors, and different packaging). They are not readily available at drugstores or supermarkets. I've never seen them go on sale, but they can be purchased at medical supply stores and some smaller owner-operated pharmacies. Occasionally I've seen them sold in sporting goods stores and at shoe stores (most recently, at Lady Foot Locker). When ordering online, be sure to order the men's shoe size that corresponds with your correct size. The Spenco soles are unisex, but in my experience they are not truly universal, in that they will only fit in women's sneakers. They will not fit in most ladies' dress shoes. The rigid quality of these soles make them unsuitable for high heels. They are molded, so they cannot be cut to size. Spenco soles are more expensive than Dr. Scholl's, but their quality is superior and they last quite a while. My only complaint, really is that for a product that touts itself as an "arch support", the support that it gives to the arches does not hold up well, at all.