I am currently using a wizard. I was wondering, if I decided to take a feat that would allow me to use heavier than light armor, would that affect my spellcasting?
I thought I read something about it in the rule book but I can't find it.
Rules for casting in armour can be found on page 201 of the PHB and are as follows:
Casting in Armour
Because of the mental focus and precise gestures required for spellcasting, you must be proficient with the armour you are wearing to cast a spell. You are otherwise too distracted and physically hampered by your armour for spellcasting.
The Lightly Armoured, Moderately Armoured, and Heavily Armoured feats all give you proficiency with their respective armour categories. This means that you would be able to cast spells if you take one, two, or all three of these feats and are wearing the appropriate armour.
Page 201 of the PHB says that you must be proficient in the armor that you are wearing in order to cast the spell.
That being said, there is a Medium Armor feat (Moderately Armored) that you can take to upgrade from light armor. There is also a Heavy armor feat (Heavily Armored), but it requires medium armor proficiency.