Plastic. The standard material for complex-shape components. Low-cost, light-weight, and formable but weak in many ways. Relatively low strength. Weak when hot. Brittle when cold. Degrades under UV light. Good isolation properties. Thermal insulation. Electrical insulation. Chemical insulation.
Wood. The standard material for home construction. Moderate cost, weight, and strength. Comfortable texture. Biodegradable. Flammable. Worn-out surfaces can trap bacteria and residue.
Metal. The standard material for strong, durable applications. Variable cost, heavy, strong. High thermal conduction. Normal surfaces are cold to touch. Heatsink applications. Forms oxides like rust. High electrical conduction.
Glass. The standard material for transparent and optical applications. Excellent transparency. General-purpose glass has excellent UV-B light absorption. Can be tinted and custom-formed to absorb, refract, and reflect different types of light.
Fabric. The standard material for clothing. Excellent flexibility with good tensile strength and breathability.
Ceramic. The standard material for high-temperature and weathering applications. Excellent heat and chemical resistance.
Rubber. The standard material for shock absorbing, sound dampening, elastic sealing, and high-friction applications.
Copper. The standard metal for electrical wiring. Excellent electrical conductivity bested only by silver.
Aluminum. The standard metal for light-duty industrial applications. Light-weight and strong with good corrosion resistance from its naturally-occurring oxide surface layer. Relatively low hardness and impact resistance, allowing easy scratches and dings. Will corrode if the oxide layer is damaged. Good electrical and thermal conductivity. Popular in aerospace and marine applications for its high strength-weight ratio and chemical resistance. Common alloys are 6061 (better formability and corrosion resistance) and 7075 (better strength and hardness).
Iron. The standard metal for heavy-duty industrial equipment. Moderate strength and production flexibility (ex. cast iron) with great vibration dampening properties for a metal.
Steel. The standard metal for industrial construction. Strong, but hard to machine, form, and cast.
Stainless Steel. The standard metal for high-strength, corrosion-resistant applications. Far better strength density, hardness, and impact resistance than aluminum but far worse strength-weight ratio. Excellent corrosion resistance across the whole material.
Bronze. The standard metal for solid low-friction applications. Good self-lubricating properties. Be warned that lead bronze alloys are toxic. Use aluminum bronze alloys where air/touch exposure is a risk; Al-Br bearings are commonly used in gym equipment.
Magnesium. The standard metal for light-weight applications. 30% lower density than aluminum with similar strength. Corrodes easily in wet conditions. Strength drops off with higher temperatures. Highly flammable in powder form.
Neodymium. The standard metal for permanent magnets.
Nickel. The standard metal for wear-resistant plating and producing corrosion-resistant alloys such as stainless steel.
Zinc. The standard metal for sacrificial corrosion-resistant plating. Use zinc alloys to avoid whiskering (dendrite crystal growth) during electrodeposition.
Cadmium, Lead, Mercury. Heavy metal and cumulative biotoxin. Strongly discouraged unless their unique characteristics are absolutely required.
Plastics & Resins
Low Density Polyethylene (LDPE, SPI-Code 4). The standard plastic for soft, flexible parts. Light-weight and flexible. Good chemical resistance. Used for plastic bags, films, and containers.
High Density Polyethylene (HDPE, SPI-Code 2). The standard plastic for sturdy parts. Far greater strength-weight ratio than LDPE. Good chemical resistance. Used for plastic barrels, boxes, general-purpose containers.
Polycarbonate (PC, SPI-Code 7). The standard plastic for transparent impact-resistant applications. Also known as shatter-proof/bullet-proof glass.