High tech low tech: Plastic Armor

[DanHoward]

Originally Posted by Anthony

Thicker, yes. Heavier, no. A UHMWPE/HDPE level III plate is less than half the weight of a level III steel plate (it's about three times as thick, though).

I didn't think we were talking about advanced composite plastics that were specifically designed for ballistic protection.

[oneofmanynameless]

How does plastic stack up against hardened leather? from just handling and messing around with both things it seems like hardened leather is heavier.

[Anthony]

Originally Posted by DanHoward

I didn't think we were talking about advanced composite plastics that were specifically designed for ballistic protection.

If you're serious about making plastic armor, you're going to make it out of plastic that's good at being armor. If you're a hobbyist trying to make good looking stuff out of plastic you're going to wind up with costume pieces. If you're a SCA fighter making plastic armor you're going to wind up with stuff that is okay vs crushing and cutting and fairly useless against impaling. The same if you're trying to use sports gear as armor.

[Tyneras]

Originally Posted by oneofmanynameless

How does plastic stack up against hardened leather? from just handling and messing around with both things it seems like hardened leather is heavier.

It will be heavier and thicker than the plastic (Pyramid #3/52) but how much depends of what "plastic" you are comparing it to. Are we talking stuff like a milk jug or lawn furniture is made of, or laminated fiber reinforced resin polycomposite whoodilly-who?

[Polydamas]

Originally Posted by DanHoward

I didn't think we were talking about advanced composite plastics that were specifically designed for ballistic protection.

Also, performance against penetration from supersonic bullets is not a very good guide to performance against arrows, axes, or clubs. The physicist in Washingon State worked out different 'back of the envelope' formulas for arrows and bullets.

The modern plastic armour I am familiar with is only designed to stop Cr damage, I never tried cutting or shooting arrows through it. Plastics can catch fire or melt and cling to skin which can be a very bad idea in any low-tech context, especially combat. Wearing modern wool-nylon or wool-polyester blends around campfires is a bad idea for that reason.

[Anthony]

Originally Posted by Polydamas

Also, performance against penetration from supersonic bullets is not a very good guide to performance against arrows, axes, or clubs.

While this is true, plenty of bulletproof level IIIa armors also pass knife resistance standards, and anything higher level will be impervious to any hand weapons usable by humans.

[Polydamas]

With enough mass and bulk, any material can stop any projectile. I am pretty sure that per square foot, level III body armour is heavier than any armour worn against muscle-powered attacks.

The physicist's other back-of-the-envelope point was that the physics changes when homogeneous armour is at least as thick as the projectile is wide. So again, the best material for thick plates vs. supersonic bullets may not be the best material for thin sheets vs. thrown spears.

[Pursuivant]

Originally Posted by AlexanderHowl

Plastics tend to provide semi-ablative armor if rigid because they are designed to break before their wearer breaks, absorbing any damage at the cost of their structural integrity. Modern steels are much better for low tech armor, as they provide three times the DR for the same mass.

This is particularly true for things like bicycle or motorcycle helmets which are designed to protect against one really solid blow before being replaced. The same is true for some construction helmets, especially the cheaper "bump helmets."

[Pursuivant]

Originally Posted by oneofmanynameless

How effective would low tech armor made out of modern plastic be?

It depends on the type of plastic you're using, how thick it is, and how you form it.

Improvised armor made from a HDPE plastic bucket, like you'd get at a hardware store or by scrounging behind a restaurant, might have DR 3 vs. corrosive damage, DR 2 vs. crushing or cutting, and DR 1 vs. anything else. Treat it as being semi-ablative and flexible vs. crushing or cutting damage. In cold weather treat it as ablative or even brittle. As a guess, call it 1 lb./square ft.

If you're manufacturing protective gear out of CPVC or similar hard plastic, it might have DR 7 vs. most corrosive and crushing damage, DR 3-5 vs. most other types of damage. Treat it as being semi-ablative and reduce effective DR 1 vs. kinetic attacks if it is exposed to temperatures over 100 *F (40 *C) for long enough that it gets warmed through. It might have a weight of 8-9 lb./square ft.

Originally Posted by oneofmanynameless

How heavy would it be? What would it's DR/Cost/Weight/Don by compared to the armors on Lowtech pg. 110-111? Would it have reduced DR against any particular damage types? etc.

As a very loose rule, soft plastics weigh about as much as boiled/waxed cuir bouilli leather armor of the same thickness. They do pretty well against crushing damage, marginally well vs. cutting, and are depressingly vulnerable to impaling/piercing. They laugh at many forms of corrosive damage and are semi-flammable vs. burning attacks.

Treat hard relatively brittle plastics like plexiglass like wood - brittle and ablative with maximum DR of 2-3. They are hit and miss when it comes to corrosive protection, in some cases materials like rubbing alcohol can damage them

High quality, impact resistant, hard plastic shaped by someone who knows what they're doing might result in a 10-20% weight savings over leather with a 10-20% increase in DR. Think sports equipment and protective gear.

Thick hard plastic specifically designed to survive hard impacts approaches mild steel in DR value and has approximately the same weight but is much thicker.

The virtue of plastic is that it's much less vulnerable to rust and rot than steel or leather and, with some exceptions, it's far more resistant to corrosive damage. At TL7 and above, plastic is cheap compared to leather and is usually competitive with steel or aluminum. Additionally, some sorts of plastic are free for the scrounging.

While most plastics start to soften up when temperatures rise about 100 *F/40 *C, hard plastics like CPVC have flash points well above the temperature required to set wood on fire and they tend to self-extinguish. This means that they have resistance to burn damage equivalent to metal except that they are effectively semi-ablative vs. heat since the material deforms more easily than metal would. Soft plastics might ignite and melt, effectively setting the wearer's armor on fire.

[Polydamas]

That is another good point. Plastic armour does not rot, and it is much more resistant to fungus, mildew, and losing its shape in heat than leather. Its a very low-maintenance armour, whereas big pieces of leather armour rarely last decades. That is one reason why people like it for combat sports: they don't have servants to do the boring work.