Which Antifreeze? Why? Answers here ...
 

This is a YouTube video on antifreeze / coolant. It's VW-specific but contains a lot of useful information that can be applied to any make of vehicle, including Japanese-made Miatas. Well worth a few minutes of your time, explains what different formulas exist and why, and also why you should be using a specific coolant with a specific vehicle. Enjoy.

I should add that it's 17 minutes, although once they go to the VW part #'s at the end, you can probably stop viewing if you want.

I get the ford stuff and mix it with distilled water. Same as the mazda stuff except its concentrate, not pre mixed

https://rallyways.com/5842/best-miata-coolant/