#protoflesh

In a way, it can be said that Cybertronians have both exoskeleton and endoskeleton. They have bone struts for holding things in place, and at the same time their frame is covered with hard metal shells. These shells are armorplates because well it's an armor???

Armorplates are divided into two types according to hardness, thickness, and flexibility.

Armorplates

Outer armorplate is hardest and thickest. This part has most pigments so it appears extra colorful compared to the rest of the body parts. Primary outer armor is the thickest and hardest, as this is the part that forms the shell of one's vehicle form. Secondary armor contributes more to the protection of root form. It is still pretty tough, but it's usually thinner and sometimes segmented to enable movements.

Inner armorplate focuses more on mobility, so it is thinner and more flexible than outer armorplate. Primary inner armor is usually covering upper arm and thighs. Secondary inner armor is protecting midsection, and it is almost always segmented because that part moves a lot.

Protoflesh

With no armorplates, a Cybertronian looks like a creepy ball joint doll made of nanite muscles. There are three types of protoflesh: Squishy bit, Stretchy bit, and Stiff bit.

Squishy bits are the softest, as they are mostly made of inactive nanites and very tiny metal bits. Together they form a structure that is very similar to muscle fibers found in human body. Squishy bits are also squishy because they are surrounding delicate inner structures like pistons and gears, so that they wouldn't dislocate easily from outside impact. Also, it is squishes into vehicle shape when Cyberteonian transforms to vehicle mode.

Squishy bits are also the most sensitive. In case of fingers, the squishy bit exists directly below the thin armorplate to sense things better.

Stretchy bits are like tendons made of really tough alien rubber, but not exactly matches 1:1 to human tendons. They exist to keep the squishy bits in place, especially during transformation. They stretch when a Cybertronian transforms into a vehicle, and they snap back to place when transformed back to root form.

Faceplates are considered as part of stretchy bit because well they stretch a lot to make various expressions, but they are more like inner secondary armorplate in terms of texture and toughness, as they are the only exposed protoflesh part.

Stiff bit is stiff. That's why it acts as secondary support structure (primary support structure is bone struts). They are like super hard alien plastic. They cover the places that needs extra extra protection, such as chest (right above spark chamber), front arm (this is where Cybertronians usually install their tools and guns, so the squishy and stretchy bits need to be protected from those), wherever the wheels are (in order to absorb the shock when driving), feet (in case of fliers, to absorb the shock of landing) and so on.

The stiff bit that protects processor is extra thick for obvious reasons.

So.... does that mean armorplates are essentially robot clothes?

No, they are their skin. They can take it off without pain, but why would they unless there's medical emergency?

Cybertronians come to the world with full set of armor. They take shower in their armor. They sleep in their armor. They even [EXPUNGED] in their armor. The armored form is their complete form. They don't need to cover themselves with fabrics or wear shoes like humans do, because they are already fully protected from birth. Though Mirage would like to say otherwise regarding footwear, because he'd been stepping on some unspeakably nasty stuff

Yes, "nude" is inappropriate in Cybertronian standards too, but not because it's 'sexy' or anything. In fact, nude is classified under 'mild gore' category in Cybertronian culture. Not wanting to see other person's exposed muscle fiber is a lot different from not wanting to see other person's "business down there".

Also, protoflesh is very vulnerable to outside hazards. A simple skin disease like rust can send a bot into operation chamber if it infects the entire chunk of ferrofluidal muscle. Stiff bits can be broken if a bot suffers direct impact to it. Everything will feel either too painfully hot or too painfully cold, because the protoflesh is not used to sensing things directly. A warm afternoon sunlight might feel like hyperthermal death ray.

Cybertronians, despite concerns from most doctors, often take off parts of their armor for regular maintenance. It is especially important to do so when they need new paint job.

Walking in on them in the middle of maintenance is far worse than walking in on someone changing their underwear, because Cybertronian processor is programmed to feel instant vulnerability when a piece of their armor is not on their frame.