Xjyuk

When you give a companion armor he/she will wear whatever has the highest armor rating regardless of what sort of enchantments it may possess. You also can not remove your companion's basic apparel. So when you get a companion who is a mage, such as J'zargo or Aranea, and you want to equip them with robes they will not wear them because the robes you give them and the robes they already have on both have an armor rating of 0. I've already tried giving them armor with a higher rating so they will take off their basic robes and then take away the armor, but they just put the basic robes back on. Does anyone know how to get their mage companions to switch robes? I'm trying to get J'zargo to wear the Archmage's Robes instead of his Novice Robes of Conjuration.

If you AREN'T on the pc, the only way to get J'zargo to wear those robes (as I did on my xbox 360) is get pickpocking to 100 for the "PERFECT TOUCH" perk which allows you to steal his default armor and thus allow him to wear the archmage's clothes, that's how I got it anyway.

If you are playing on PC, there are several answers to this question you might find helpful. Notably:

You can remove all of your companion's default armor by opening console with the ~ key above tab on your keyboard then by clicking on your companion, in which case Lydia, and typing removeallitems and pressing enter. Now you will be able to place what ever you want on him/her. As a warning, if you remove their armor & weapons they will lose their infinite arrows and you will need to replace them every time she/he runs out.

Important: Make sure to remove all items from your companion's inventory before doing this because you will lose them!

and...

If you are on PC, TCG Tradable Companion Gear might help you out.

The second being a link to a mod that let's you liberally change whatever gear your followers are wearing.

give her the items, open the console, click onto the follower and type:

showinventory

you should now see a list of all items plus their id-codes.
Now just type:

removeitem [id of the item] [number of items to remove]

so it should look something like removeitem 0004a26b 1

Note: This id is just some creation of mine, i've got no idea what object it could be.

The id is a hexadecimal (contains a to f) number of 8 characters.

This way is better than removeallitems, for you can pick those items you want and trading items to follower seems to reset theit default equipment.

If you're on PC, you can use the console for this, much like most other Skyrim problems. If you're on Xbox 360 or PS3, you're probably screwed, much like most other Skyrim problems.

In the console, you can type help "Archmage's Robes" to get the item ID of the Archmage's Robes (or any other items you may want to equip to people later).

For the Archmage's Robes in particular there are two different versions (quest outcomes I guess?). Without +50 magicka its ID is 0007C932, and with +50 magicka it's 0010F570. Then you can open up the console, click on J'zargo, and type equipitem 0010F570 to equip the robes on him (or the other ID if you have the other version).

If he doesn't have the robes in his inventory, or if he has the wrong version, that command will actually conjure up a set of Archmage's Robes out of thin bytes and give and equip them to him.

I can't speak to Aranea as a follower as I've never taken her as one. I have taken J'zargo as a follower, though. He has no level cap(if you are level 150, so is he). At higher levels he has high to max heavy armor skill and will gladly equip some nice high quality heavy armor(well tempered and enchanted is best).

NPCs don't care about enchantments, they only care what a piece's armor rating can do for them. Also, most followers(maybe all) cannot take advantage of fortify skill enchants as only the player has a special hidden perk that allows you to use them. They can use resistances, stat increases and extra regen.

When I took J'zargo as a follower I gave him extra magicka on his gauntlets, extra regen on his armor and helmet, elemental resist on his boots and a combo of elemental and magic resists on his necklace and ring. He still only uses novice and apprentice destruction spells in combat, though. With heavy armor, he also isn't that great of a pack mule since he can't carry that much.

I found you could do in a very long winded way if you don't train in sneak (on the ps4). So marry the follower, get a home where they can set up a shop, give them some armour so they'll wear that instead, go outside and enter your followers shop and the only items they should have for sale are the ones in there inventory at the time as well as there base outfit so buy it from them and then place the outfit you want them to wear in there inventory then take armour from then and boom they should be wearing it.