i got a worn ttsko jacket with worn gorka pants, and i have not got overheating problems...(running around at day when it's dry weather)
but i have noticed differnt conditions of the cloting lead to differnt states of freezing (my pristine jacket got raped by a zombie at night when its was raining and i started freezing) so maybe this might be the reason its fine for me
also i'm always nicely hydrated, don't know about you though
some more info could help the devs...

Yeah that's what is supposed to happen when you wear a jacket, you will warm up.

Hello nerobp,
I have tried this and did not have issues with overheating because of this jacket. As the commenters above have said, this could be affected by state of the jacket, your hydration level and other factors.
I will keep this in mind and be on a look out for possible issues, but for now I believe there is no bug here.
Thank you for your report,
A.