Heavyweight cotton. Good qualityMy husband really liked the fit, material and look of this shirt. The (prewashed) cotton is very soft and washed and dried well in the machine.I was looking for a 100% cotton polo that was truly heavy weight, but this shirt disappointed. It’s thinner and softer than I hoped. I’m 5’8” and 170lbs and I’ve never had a toned/sculpted mid section so I look for shirts that don’t cling, and that usually requires a thicker cotton fabric that has some body. This shirt was better than some, but was still too sheer/soft/clingy for me. Although the fabric was too thin, the shirt was cut big enough through the mid section that it wasn’t either tight or overly loose. Also I disagree with the reviewers that say this shirt runs large. I wear either size medium or large depending on the cut of the shirt, but for this one I should have ordered medium. I do agree with the reviewers that say the sleeves are too long. I returned this shirt and will keep looking for a heavier weight shirt like those that were made years ago.I like these shirts, but. . . I ordered my regular size (XL) and they were too small - fit like a Large. Ordered 2XL and two shirts were okay but the red one is more like a 3XL. So beware. Otherwise the shirts are very nice and are well made with good material.I use to buy JC Penny's. St. John's Bays polo shirts and loved the heavy material, the shirts lasted for years, then they went cheap and thin materials and I've spent I don't know 6 years looking for someone who made a nice heavy cotton polo shirt and ladies and gentlemen, I found them. I have 5 of these shirts, one yellow, one green and three black and they fit great, wear great, I am happyThis shirt was just what I was looking for. The material is substantial, the fit is generous but not too much so, the sleeves are a nice length, not like a lot of modern polos that have very short sleeves. This shirt is just right.The polo arrived yesterday and, unfortunately, it definitely is not soft...at all. It is mesh weave and will need many washes to soften it up. The buttons are colored; not clear or white. I'm sending it back.I paid much less for shirts like this that were much better. The sleeves are way too long, I am not really happy with these shirts. Probably will send them back