Clearly, you are not talking about a full plate armor to be used by a Gelatinous Monster.
Let me first differentiate Piercing attacks from <PERSON> attacks:
Piercing attacks they provide a greater pressure per surface point, examples: lance, arrow, pickaxe. That characteristic allows the attack to spread the object body (open a hole).
Blunt attacks they are in fact the same, except that the affected area is bigger than a piercing attack, examples: Warhammer, club, mace. The main focus is on the impact, the stopping power, the amount of energy transferred to the object body.
For a full explanation on the calculations of kinetic energy transfer and ballistics please refer to this article.
To protect from piercing attacks is necessary to spread the affected surface (like a bullet-proof vest) so instead of having the pressure in a small surface, you have it spread all over the object body, lowering the pressure and the piercing power.
To protect against blunt attacks it's the absorption of the impact (like mentioned on the car impact example on the previous answer)
Here are some examples of what could protect from blunt attacks:
1) Padded Armor/Skin/Shell: This will not necessarily be a hard shell, but an absorption foam-like structure (jumping on top of a mattress)
2) Fluid surface: Sand-like or Jelly-like exterior, these will spread the energy of the impact to several tiny particles converting the kinetical energy into heat(friction). 561
This is also useful for piercing attacks if the friction can destroy the projectile.
3) Reflection of the energy: Any structure that will move the kinetic energy pass the object body like a super slippery surface in an angle. As an example, we can use the gladiators oiling their bodies to avoid grappling and to deflect punches.
Hint: Consider the crack resistance as well, like the amount of energy that needs to be transferred to break the structure of the object body (a good example is a bone, it is very resistant, but a material with a harder structure will crack it easily Hammer > Skull)
Creating a list of the structures that are harder to crack is a good way to define the protection level it will give you. (It is a lot easier to cut a steel sheet than blunt a hole on it because the material is malleable) 621