Armor is protective, but it can also hinder. Here are commonly used rules for armor.
ARMOR CHECK PENALTY
Any armor heavier than leather hurts your ability to use some skills. An armor check penalty is the modifier that applies to Balance, Climb, Escape Artist, Hide, Jump, Move Silently, Sleight of Hand, and Tumble checks made by someone wearing a certain kind of armor. Double the normal armor check penalty is applied to Swim checks. A creature’s encumbrance might apply a similar check penalty.
SHIELDS
If you wear armor and use a shield, both armor check penalties apply. They stack.
NONPROFICIENCY
If you wear armor or use a shield you aren’t proficient with, you take the armor check penalty on attack rolls, as well as on all Strength-based and Dexterity-based ability and skill checks. This effectively adds Open Lock, Ride, and Use Rope to the list of penalized skills. The penalty for non proficiency with armor stacks with the penalty for non proficiency with shields.
If you have a check penalty from encumbrance that is higher than your armor check penalty, use the encumbrance’s check penalty on skills normally affected by the armor check penalty. Use the armor check penalty on checks and rolls normally penalized for nonproficiency.
ARCANE SPELL FAILURE
Armor interferes with the gestures an arcane spellcaster must make to cast an arcane spell that has a somatic component. Unless they have a class feature that says otherwise, arcane spellcasters face the possibility of arcane spell failure if they’re wearing armor and/or using a shield. A spell without a somatic component, however, can be cast with no chance of arcane spell failure. If a creature is wearing armor and using a shield, the arcane spell failure chances for the two pieces of equipment stack.
When casting an arcane spell that has a somatic component, arcane spellcasters subject to arcane spell failure for the armor they’re wearing must roll d%. If the result is equal to or lower than the chance for arcane spell failure, the spell is ruined. The caster still expends the prepared spell or the slot required to cast the spell.
SPELL COMPLETION ITEMS
Activating a scroll or any other spell completion item is like casting a spell for the purpose of arcane spell failure. An armored creature that activates a scroll by using Use Magic Device has the normal arcane spell failure chance.
SLEEPING IN ARMOR
When you sleep in medium or heavy armor, you’re fatigued the next day. Sleeping in light armor doesn’t cause fatigue.
DONNING AND REMOVING
The time required to don armor depends on its type. See the following table.
| Armor Type | Don | Don Hastily | Remove |
| Shield (Any) | 1 move action | N/A | 1 move action |
| Padded, leather, hide, studded leather, or chain shirt | 1 minute | 5 rounds | 1 minute1 |
| Breastplate, scale mail, chainmail, banded mail, or splint mail | 4 minutes1 | 1 minute | 1 minute1 |
| Half-plate or full plate | 4 minutes2 | 4 minutes1 | 1d4+1 minutes1 |
- If the wearer has some help, cut this time in half. A creature doing nothing else can help up to two adjacent wearers. Two wearers can't help each other don armor at the same time.
- The wearer must have help to don this armor. Without help, it can be donned only hastily.
Don
This column tells how long it takes to put the armor on. (One minute is 10 rounds.) Readying (strapping on) a shield is only a move action.
Don Hastily
This column tells how long it takes to put the armor on in a hurry. The armor check penalty and armor bonus for hastily donned armor are each 1 point worse than normal.
Remove
This column tells how long it takes to take the armor
off. Loosing a shield (removing it from the arm and dropping it) is only a move action.
