I'd disagree with that. I have a few of these t-shirts now for holidays. I 'glow' quite a lot in hot weather and these are a big help. They are definitely thinner and lighter than my golf tops, same material. It is not surprising. Golf tops are designed for use in all 4 seasons so they will be a compromise weight. The running tops are designed to be worn for people who are going to sweat more, get hot etc. so they only have to be designed to cope with a hot situation.The only difference between golf shirts and running shirts is the collar nowadays. All my golf shirts are polyester, or polyester/elastane blend, exactly the same as the sports tops that I own. In fact the collar can help keep the sun off your neck.