Vanilla Morrowind has a big problem with Medium Armor. For some reason the developers decided that the best Medium Armor set (Indoril) should offer less protection than the best Light Armor set (Glass), despite being heavier. The DLCs rectified this a bit by adding the powerful Royal Guard Armor set, but it's still only slightly stronger than Glass. Tribunal also adds the Adamantium set which is worse than Glass, and Bloodmoon adds the Ice/Stalhrim set which is on par with glass (despite again, being much heavier). Given that these Medium Armor sets are meant to be special and a challenge to obtain, it didn't make sense to me that they'd offer such underwhelming protection.
To address this, this mod increases the Armor Rating of the Adamantium, Ice, and Royal Guard armor sets to make them all exceed Glass Armor's quality. There's a few other mods that try to do this same thing, but I feel they go too far overboard changing enchant values and armor health and all these other things. This mod is meant to be as simplistic as possible in its adjustments.
I did go ahead and change one enchant value though, and that's for the Left Aamantium Pauldron. The Right Adamantium Pauldron has a default enchant value of 10, whereas the left one only has a default enchant value of 3, which doesn't make any sense, so I've brought the left pauldron's enchant value up to 10 to match the right one.
The latest version of this mod also improves the Armor Rating of the Bear and Snow Bear armors from Bloodmoon. In vanilla, both sets had the same Armor Rating as their light armor counterparts (Wolf and Snow Wolf) despite, yet again, being substantially heavier. Although the Bear sets aren't meant to be better than Glass, I think they still deserve to get at least a small upgrade (especially given how nice looking the sets are!)

The following chart displays all the changes in the following format:
Old Armor Rating -> New Armor Rating

Adamantium Armor
Now on par with unmodded Royal Guard Armor. However, the helmet for whatever reason has a default armor rating of 70 so I've left this unchanged. The greaves are also unchanged because they already have the same unmodded rating as royal guard greaves.
Boots: 40->50
Bracers: 40->55
Cuirass: 40->55
Pauldrons: 40->55

Ice Armor
AKA Stalhrim. Previously on par with Glass Armor, now better than it.
Boots: 50->60
Gauntlets: 50->60
Cuirass: 50->60
Greaves: 50->60
Pauldrons: 50->60
Helmet: 50 ->60
Shield: 50->60

Royal Guard Armor
Still the best per-piece armor rating of any medium armor set, but now even more so. As far as the logic behind the improvements I've given it, each piece of Glass armor has a rating of 50 and each piece of Daedric armor has a rating of 80, so I figured I'd split the difference and put the Royal Guard Armor rating right between the two at 65.
Boots: 50->65
Gauntlets: 55->65
Cuirass: 55->65
Greaves: 40->65
Pauldrons: 55->65
Helmet: 55->65

Bear Armor
Previously on par with Wolf Armor, now better than it.
Boots: 15->20
Gauntlets: 15->20
Cuirass: 15->20
Greaves: 15->20
Pauldrons: 15->20
Helmet: 15->20
Shield: 15->20

Snow Bear Armor
Previously on par with Snow Wolf Armor, now better than it.
Boots: 35->40
Gauntlets: 35->40
Cuirass: 35->40
Greaves: 35->40
Pauldrons: 35->40
Helmet: 35->40


*Since Ice Armor is much more challenging to obtain than Royal Guard Armor, I've added an alternate version of this mod to the main file that swaps the armor rating between the two so that Ice Armor will be the best set (every piece of Royal Guard Armor instead gives 60 armor rating and every piece of Ice Armor will give 65).
*Also in the main file is an optional version that renames Ice Armor to Stalhrim Armor, to make it more consistent with the Stalhrim weapon set (and more consistent with the Dragonborn DLC for Skyrim).
*If you want Ice Armor to be the best set of medium armor AND have it renamed to Stalhrim Armor, there is a version for that in the main file as well.

Only use one version of this mod at a time, don't use multiple ones simultaneously.

Requires Tribunal and Bloodmoon