Will someone please be kind enough to explain to me about evaporation?

I'm relatively new to biking, been doing it seriuosly for about 8 months. I'm still in the process of getting all the equipment I need (at this point I need mostly clothing). I live in Scottsdale, AZ and at this time of the year the temps are generally in the 40's and 50's when I ride mid morning. I wear a sweat suit with a light jacket over it. I ride between 20 to 40 miles per ride at about 14 - 15 MPH.

When I come in from a ride I'm drenched, underwear, sweatsuit, jacket, everything. I feel like I've just taken a shower, but know that's what I really need.

I know what I'm currently wearing is not the correct attire to be biking in. What is the correct attire? I do not mean Bibs and a shirt, I'm referring to material and why.

Thank you.