I'm not sure exactly. I'm looking on amazon right now. I was thinking about some 8" wide seat with gel and that's about as far as i got. I've felt a Selle Royal seat but I didn't sit on it. I was also looking at Cloud9 seats on amazon so right now I'm not sure. Either the stock seat is fine and I need to break my ass in or the seat is a inch or two too small. My sit bones are 130mm and the brompton is the H type so Im as upright as you can get. Pretty sure I need a wider seat than 6".