While the classic Houdini Jacket uses an ultra-lightweight 100% ripstop nylon material, the Houdini Air Jacket uses a double-woven fabric with two types of yarn: nylon and polyester. By incorporating about 10% polyester yarn into the fabric, a slight unevenness is created on the back side. This seemingly small detail eliminates the characteristic crispness and clinginess of 100% nylon, resulting in a very "smooth" feel. This is noticeable even when your skin is dry, but the most significant difference is felt when wearing it over a short-sleeved base layer and sweating! Many people have experienced the "cling" of nylon when wearing a 100% nylon wind shell against sweaty skin, but the addition of just 10% polyester yarn reduces that clinginess! This subtle difference in fabric adds to the comfort, making the Houdini Air Jacket feel more relaxed, even though it's the same size and slim fit as the other JKT. I believe the difference in texture resulting from the fabric is the biggest factor, but I also think the cutting and sewing patterns contribute. Whether raglan sleeves are better or set-in sleeves is a matter of personal preference, but I personally prefer the raglan type because it doesn't restrict the shoulders, and your arms can move easily even when layering with a fleece and the shoulders become bulky. Compared to the 100% nylon HOUDINI JKT, the polyester-blend HOUDINI AIR JKT weighs about 13% more, approximately 14g, based on a size M measurement. When you hear that the weight has increased by 13%, it might sound heavy at first, and it might be a critical issue for those who prioritize ultra-lightweight gear, but in terms of grams, it's only an increase of 14g. Considering the improved comfort during wear, wouldn't you say the benefits outweigh the drawbacks? Why not consider it? Measurements (approximate): Width: 50 cm Length: 75 cm Sleeve Length (from center back): 86 cm Please note that these measurements are approximate due to amateur measurement methods.