Elite Dangerous: Module damage vs Bulkheads

Hull reinforcement test

	Asp Explorer 1678	Asp Explorer 378	Imperial Cutter 1690 E modules	Imperial Cutter 1690 A modules	with Mirored armor 2370 (A)
Small cannon	9	10	5	4	5
Medium cannon	23	25	11	9	14
Large cannon	47	50	27	23	34

No matter which module: Power Plant, Frame Shift Drive or Drive

Kinetic weapon test

Imperial Cutter	Lightweight	Reinforced	Military	Reactive	Mirrored
Small cannon	4	4	4	2	5
Medium cannon	9	9	9	6	14
Large cannon	23	23	23	14	34
Huge cannon	37	37	37	22	56

Thermic weapon test

Imperial Cutter	Lightweight	Reinforced	Military	Reactive	Mirrored
Large Pulse Laser	2	2	2	3	1
Large Burst Laser	5	5	5	7	2

As you can see even 4x more armor points will only slightly increase module protection, A rating modules are better protected than E and modules on Imperial Cutter are better protected than on Asp Explorer.

Regarding bulkheads Lightweight, Reinforced and Military are exactly same, Mirrored will offer 50% better protection against Thermic weapons but it will be 50% less effective against Kinetic and Reactive armor is exact opposite.

Video