iPhone 5 Factory Reset to iOS8

[guy weaty]

My iPhone 5 was upgraded to iOS10. If I factory reset my phone, will it downgrade to iOS8?

 

[Applejuiced]

No.
you can only restore to the latest firmware version signed.
iOS 10.0.3

 

[eyoungren]

My iPhone 5 was upgraded to iOS10. If I factory reset my phone, will it downgrade to iOS8?

A common mistake is to symbolically attach the words "Factory Reset" to what Apple labels "Erase All Contents and Settings". Why people do that, I don't know. Apple has never used those words.

Factory reset implies a return to the firmware the device came with, but if you look inside the Settings app you will never find the words "Factory Reset".

I bring this up because Erase All Contents and Settings is the actual command and it does exactly that. It erases all contents and settings and restores the device to the highest currently signed firmware.

You can't find the words "Factory Reset" on any Apple device, because it doesn't exist - either the ability to do that or the words themselves.