They are Anderson 100 series windows. The are a fiberglass composite product. Been using them 5 years now and have had wonderful results. The price point is pretty attractive as well. They don't swell and twist like vinyl and they are very rigid. The large window in that picture is one piece all mulled together. I've also done them where I buy 6 individual windows and frame and trim in between. Probably ends up close to a wash in price but gives you a little different look. I prefer the second route myself. Let me know if you have any other questions