PA does not have a helmet law. I just think people are crazy not wearing one! I've seen people ride that twisty road by Port Jervis without a helmet.
As for your issue with heat, try soaking a t-shirt in water and putting that on, before putting on a mesh jacket. If your rides are long, carry water on a tank bag and pour it on your t-shirt. When water evaporates, it'll cool your skin.
As summer winds down, and the weather gets cooler, you can wear a textile or leather jacket.
Wear gear all the time. Think about it. Ride a bicycle and purposely fall off at 10mph. You're going to bleed, right? Now do that at 40mph and hit a curb while you're at it. It's going to hurt a lot more. In the real world, you'll never know when some dipshit person texting will swerve into you and make you lose control and go down.
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Ghostt - I'm glad you posted that story up along with those pictures. It's a good reminder for all of us...