Can someone please explain how defense works?

Not sure if this is accurate, but it's the best I found: http://gaming-fans.com/2017/02/swgoh-a-look-at-defensive-stats-health-protection-defense/

https://forums.galaxy-of-heroes.starwars.ea.com/discussion/67830/defense-armor-calculator

Defense is like Einstein's, "Spooky action at a distance". My two cents :)

Defense is just damagr reduction. It should say how much damage % is reduced under defense on the stat card of the character

None of these posts are actually answering the question at hand. How much more damage reduction is +100% defense from Sith Trooper's unique? Does it just strait up double his armor or does it add less than that? Does it get capped at a certain point?

It doubles his modded armor. This is a lot of damage reduction. He can easily get to the 60% damage reduction level with average modding.

Use the calculator in the post above, to work out what your modded armor/resistance is by matching the percentage reduction from your stats screen and reading out the flat number the calculator gives you. Now double the flat number (if it was 400, use 800) and enter it back into the calculator and it will give you the resultant damage reduction that sith trooper will have in combat. Use 2.5x if you want to simulate for Defense Up,

"Josh_K;958930" wrote:
It doubles his modded armor. This is a lot of damage reduction. He can easily get to the 60% damage reduction level with average modding.

Use the calculator in the post above, to work out what your modded armor/resistance is by matching the percentage reduction from your stats screen and reading out the flat number the calculator gives you. Now double the flat number (if it was 400, use 800) and enter it back into the calculator and it will give you the resultant damage reduction that sith trooper will have in combat. Use 2.5x if you want to simulate for Defense Up,

Does the defense ever cap at some point? Like if he has 30% base armor, doubles it to 60% defense and then gives himself Defense up wouldn't that give him effectively 90% armor? Or does defense up only go off of base armor which would be 75% total damage reduction.

"Darth_Skywalker;958940" wrote:
Let's make this more simple, if you increase protection or health you will benefit more then say defense mods.

No ones talking about Defense mods, we're talking about defense uniques and defense up. Everyone already knows to stack protection.

Defense stat is very complicated. Gaining 100 defense or 100% defense will benefit some character way more than others.

Defense boosts on characters with already high defense is best, but as a rule of thumb it is easier to just stack protection on your character. Both protection and defense (armor) help your character survive longer, but the game tends to give you more bang for your buck with protection

"Vertigo;958935" wrote:

"Josh_K;958930" wrote:
It doubles his modded armor. This is a lot of damage reduction. He can easily get to the 60% damage reduction level with average modding.

Use the calculator in the post above, to work out what your modded armor/resistance is by matching the percentage reduction from your stats screen and reading out the flat number the calculator gives you. Now double the flat number (if it was 400, use 800) and enter it back into the calculator and it will give you the resultant damage reduction that sith trooper will have in combat. Use 2.5x if you want to simulate for Defense Up,

Does the defense ever cap at some point? Like if he has 30% base armor, doubles it to 60% defense and then gives himself Defense up wouldn't that give him effectively 90% armor? Or does defense up only go off of base armor which would be 75% total damage reduction.

Defense and damage reduction is 2 different things, how did you read the links and not understand that? Giving 100% bonus to the defense doubles up the defense value but it does not double your damage reduction because of the 'diminishing' returns. You have to actually input the values to the defense calculator to check how much it benefits each specific character.

Since you are so interested in Sith Trooper, let us look at his stats and see the effects of his unique.
As max level, his defense is 264 according to swgoh.gg.
His damage reduction comes up to 264/(264+(85*7.5)) = 29.29%.
If you doubled his defense, 528/(528+(85*7.5)) = 45.31%
So you can see that there is diminishing returns and that there isn't a need for any cap since it will never hit 100%.