At first glance, it would seem that Aftershock has greatly simplified the damage mechanics from Aftermath.

Afterall, in Aftermath you had about 7 damage types (soft, hard, universal, laser, plasma, warp and burn). In Aftershock, this has seemingly been reduced to five (projectile, energy, mechanical, burn, psi). So it would seem that they greatly simplified how the damage system from Aftermath works.
And then a player tries using plasma or laser against a target that has less energy resistance than projectile, and discovers they deal no damage.

This is because the resistances you see are averages of the actual damage types in the game, which are hidden from the player. To makes matter worse, the game doesn’t tell the player any of this, other than vague hints in the glossary, nor does it tell the player what damage category each weapon belongs to. As one can imagine, this can result in some rather frustrating scenarios.

To see what the real damage types are, one has to unpack the gamedata.vsf file and find the equipment.txt and damagetype.txt files.

There’s a guide on how to do it here :
http://www.strategycore.co.uk/databank/games/ufo-aftershock/modding-guide/

According to the damagetype.txt file, the true damage types and their categories are :

Projectile :
Soft – Covers most ballistic ammunition

Hard – Covers AP ammunition and, oddly enough, flechette rounds.

Energy :
Laser

Plasma

Warp

EMP – Does not exist in the game, but still used to calculate resistances. This means that the resistance stat you see is highly inaccurate. A Starghost Defender, for example, would have 95% energy resistance ((0.95+0.95+0.95)/3) if it weren’t for EMP damage being included. The current calculation for the Defender is (0.95+0.95+0.95+0)/4 = 0.7125 = 71%.

Mechanical
Blade – Melee weapons

Sonic – Despite using energy cells and is under the energy part of the glossary, it is considered by the game to be a mechanical type weapon

Explosive

Burn
Burn – incendiary and acid weapons

Psi
Psi – Psi projectors and the reticulan blaster

To calculate the resistances one sees in game, one takes the resistance to each damage type and divides it by the number of items in the category. The game does not round off the values; what you see is the first two decimal places in percentages.
Using the starghost defender as an example again, it has a 90% resistance against soft damage and 75% resistance against hard damage.
So the game calculates the defender’s projectile resistance as ((0.9+0.75)/2) = 0.825 = 82%

The equipment.txt file lists the stats of all armour and weapons in the game, including their resistances and damage types.

Each piece of equipment in the game is divided under sub equipment records, with each subrecord having it’s own name. It starts like this :

SubEquipment RECORD
id INT 274
name STR
The damage type is for each weapon is given by the “damage STR” line, and resistances for each suit of armour (not just the ones players can use, what the enemies use as well) are under “ListOfProtection ARRAY”

It should be noted that the values you see under the protection array denote how much damage an enemy or piece of armour receives, if it says
Soft"
FLT 0.75
That means the unit takes 75% soft damage, giving it a resistance of 25%.

So, looking at the protection array for a Starghost Cloud :
ListOfProtection ARRAY 13
;"Soft FLT 0
;"Hard" FLT 0
;"Laser" FLT 0.1
;"Plasma" FLT 0.1
;"Warp" FLT 0.1
;"Sonic" FLT 0.4
;"Blade" FLT 0
;"Burn" FLT 0
;"Explosive" FLT 0
;"EMP" FLT 1
;"Psi" FLT 1
END_OF_ListOfProtection

So, it takes no damage from Soft and Hard damage types (hence the 100% projectile resistance).
10% damage from laser, warp and plasma but 100% damage from EMP (which doesn’t exist).
No damage from Explosive and blades but 40% damage from sonic weapons.
It has immunity to fire but no immunity at all against psionic attacks.

So it terms of what you see in game :

Projectile = (1 + 1)/2 = 1 = 100%
Energy = (0.9+0.9+0.9+0)/4 = 0.675 = 67%
Mechanical = (1+1+0.6)/3 = 0.867 = 86%
Burn = 1 = 100%
Psi = 0 = 0%





I hope this helps in understanding how the damage system works in game.