I've have an old pair of Rainbows and wanted a newer "going out" pair. When I ordered, I couldn't remember the size of the last pair, so I measured my longest foot. It came in exactly at the 8 1/2 size. I normally wear a size 9 shoe so I went with the larger size because I had read that Rainbow sizes ran small. I have short toes which may play in to it being large, but my heel was further from the back than I wanted. I could wear these, but with the added 3 /8" at the toes, it sets me up for a trip. I've ordered the next size down which should be too small, but I believe that's the size of my last pair which was a single layer collegiate pair but perfect. With that being said, I love my Rainbows. I know it sounds strange but I have Planters Fasciitis. At it's worst, these were the only shoes I could wear with any level of comfort. I've had this problem for over a year and can't shake it even by adding pads to other shoes. It's nice to have something to slip on for around the house. They're too grungy to wear out.Rainbows are very tight and uncomfortable when you first get them and you have to break them in. My husband and I got our first pair at the same time. I'm in mine all the time around the house and they're soiled but in good shape. He hasn't even broken his in yet. I keep telling him how comfortable mine are so he's decided to give it a try. My son had a pair for years and wore them until the toe had worn all the way down to the pavement. I finally bought him another pair as a gift. No questions about the quality, durability and comfort. I never understood how such a simple looking shoe could wear so good. I do now. I'll be interested if I like the double stack as well as I liked the single.