Not very thick. Doesn't get warm in temperatures below 45*. The buttons are amazing, the external materials are very nice. The inner material of the main body of the shirt/jacket is nice and medium weight, but the sleeves are THIN and won't keep your arms warm in cooler weather. They are lined with nylon and that's it. No quilted fabric. I sewed in the sleeves of an old flannel shirt to compensate and now this makes a very good shirt/jacket for cooler weather. I don't think most people would want that. Not because of the price, but if you go for it, this shirt/jacket goes from "ah ok" to OH YES I love it. The arms are a little longer than expected so if you have long arms this is for you. The entire length of the clothes is fine. I expect this shirt/jacket will be around for a few more years before it's time for a new one as it's very well made and has really good stitching. The inner pocket is a bit high but a nice addition.