Carapace Armor

Kasrkin commonly employ their own model of carapace armor use flak armor instead of carapace armor and the common Guardsmen respect them all the more for it. Pic related is one such sergeant of the 8th Cadian Kasrkin.

Carapace armour is basically Flak Armour LV2. A bit tougher, and a bit more expensive. Usually given to commissars and stormtroopers. A step down from the Void Armour of the Great Crusade era. It is currently the best armor that non augmented humans outside of the Sisters of Battle and Inquisitors can get their hands on. Rarely it will also be worn by Lost and the Damned or a well equipped PDF. Generally speaking, this is the most protection an ordinary man will get to use unless they get extremely lucky/prove useful enough to wear some form of powered armor.

Like Power Armor it has Ceramite or armaplas (perhaps plasteel, armaplas is never really explained) molded into armor plates. This also makes it much heavier and will fatigue the wearer much faster than flak armour or power armour given that it usually lacks any kind of assisted movement systems, though that isn't always the case as semi-powered examples do exist. Usually, soldiers issued carapace armor are elite units and given light genetic enhancement to bear the weight without problems.

The protection provided by a set of carapace armour varies a lot from story to story, as you'll frequently hear of normal bolter bolts punching clean through power armour (at close range) and thus should go through carapace like it wasn't even there, however on the tabletop now carapace offers some protection from the likes of heavy bolters, power mauls and autocannons, and to a lesser extent even Hellguns, Inferno Bolters and Sternguard Bolters.

It is expensive but still cheap enough that Krieg makes use of it in its own version of grenadiers who go in first and are expected to die first (along with hot-shot lasguns) so perhaps it isn't all that expensive after all and everyone is just plain too stupid (stingy) to realize that.

Scout Armor

Per usual any version that normal humans have, Space Marines will have a better version. Instead of Power Armor. Neophyte Astartes who survive the Geneseed process become Scouts are given Scout Armor(yeah it's as lazy as it sounds) and Camo Cloaks. To make themselves super stealthy instead of extra protection. (Unless your Raven Guard who sneak around in full Powered Armor. Though there is a fluff reason for that.)) Even Sergeants and Veteran Sergeants (who are members of the First Company) wear it when they volunteer in training the newbs. As unlike certain chapters. You don't become top dog be being a complete douchebag.

Deathwatch Scouts have further modifications. Upgraded with gel-passages, a re-breather system that contains both oxygen and water, auto injector gloves, a vox system, and a special coating. For enhanced mobility and extended operations while sneaking explosives or teleport homers into the homes of unlucky xenos.