Overview & Obtaining
Simple helmets offer cheap (albeit inferior) protection for one's head, but impose a move speed penalty of 0.04 c/s. The main pro of Military Helmets is the cheapness to manufacture and purchase, requiring little more than half of the materials that Advanced Helmets require, and also less than half as expensive when purchased.
They can be purchased via trading, produced at a machining table, or looted from Outlanders and Pirates.
Simple helmets must be manufactured at a machining table, which in turn requires machining to be researched in order to be constructed. A simple helmet requires 70 metallic materials (i.e. steel, plasteel, uranium, silver, gold) and 100 seconds of work (6,000 ticks) to be created, assuming baseline global work speed and no enhancements or hindrances to consciousness, sight, or [manipulation]].
Usage of different materials enhances protection offered and durability.
Conclusion and Comparison
Simple Helmets are one of the three main headgear protections available in RimWorld (the others being the advanced helmet and power armor helmet), but also the least protective out of the three. While being the least protective, Simple Helmets do have a remarkable lifespan due to the inferior damage absorption, especially if made out of Plasteel. They also impose the greatest movement speed penalty along with power armor helmets, with a 0.04 c/s penalty, whereas advanced helmets only impose a 0.02 c/s penalty. Simple helmets are intermediate in terms of mass with a mass of 2kg, whereas advanced helmets have a mass of 1.2kg and power armor helmets have a mass of 2.7kg.
The following table is an hierarchy of the combinations which a simple helmet may offer with varying quality levels (and full durability):
Prior to Alpha 17, it was known as the Military helmet. In Alpha 17, it has been renamed, received a slight buff to protection and has a changed cost.
In 1.0 it was tweaked to provide less sharp protection, but slightly more blunt and heat protection, and materials now affect armor rating.