I purchased this jacket for the added safety benefit of leather and needed something that could be used in the brutal summer heat and humidity in the south.
I have spent the last three days riding in this jacket. My rides would take place during the hottest and most humid part of the day. Ambient air temps were in the mid 90's and when you factor in the humidity the temp would be around 102-105.
The jacket performed well and would only get toasty if you were stopped at a red light. Once you got rolling 35 mph and above you could feel the air coming through the perf. I wear a moisture wicking tee-shirt so you get the cooling effect of the air hitting the shirt and it didn't take long for the shirt to dry. I will say that with the D3O back armor you don't get the full effect of the perf out back but you do have enough cooling to stay comfortable. The side stretch and arm panels do a an adequate job of flowing air and help with the overall cooling.
The jacket seems to be well constructed and with with straight seams and the industry standard YKK zips. Armor is nice in the shoulder/ elbow area and doesn't migrate while moving around on the bike. The colors( Hi Viz yellow/orange was my choice) look great. Very vivid. The leather seems to be of good quality. The jacket was a little stiff which is to be expected. Nothing a little Nokona glove conditioner application couldn't fix. The leather is now soft and pliable like I have been riding in it for 2 years.
Fit is what it should be for a sport riding jacket. The only little nit-pick are the sleeves are just a tad long. I know I needed a 44 as I'm thick through the shoulders, chest and arms. Not a deal breaker at all. Fit length wise through the torso is fine. I'm 5 10' and a buck 90 and there is no bunching of material at the waist. The adjuster took care of that.
If you live in a hot and humid summer time climate I would recommend this jacket as a major upgrade from the mesh/ denier combo. Great job STG for adding this to your Cortech line of gear.