Environmental factors:

Climate: Will the part be exposed to extreme temperatures, sunlight, rain, snow, or other harsh weather conditions?
Chemical exposure: Will the part be exposed to chemicals, solvents, or other potentially damaging substances?

Part requirements:

Strength and durability: Does the part need to withstand physical stress, impact, or wear and tear?
Flexibility: Does the part need to be bendable or resilient?
Weight: Is lightweighting critical, or can the part be heavier?
Aesthetics: What desired color, finish, or transparency is needed?
Budget: What is the cost constraint for the material?
Here are some common outdoor-suitable plastics and their key characteristics:

1. High-Density Polyethylene (HDPE):

Pros: Highly durable, weather-resistant, good chemical resistance, affordable, widely available.
Cons: Not as strong as some other options, susceptible to UV degradation over time.
Examples: Outdoor furniture, playground equipment, storage containers.
2. Polypropylene (PP):

Pros: Good strength, lightweight, good chemical resistance, good UV resistance.
Cons: Not as flexible as some other options, can become brittle at low temperatures.
Examples: Automotive parts, medical equipment, food packaging.
3. Acrylonitrile Butadiene Styrene (ABS):

Pros: Good strength, impact resistance, weather-resistant, can be painted or glued.
Cons: More expensive than HDPE or PP, can become brittle over time.
Examples: Helmets, luggage, automotive trim, building materials.
4. Polycarbonate (PC):

Pros: Excellent strength, impact resistance, UV resistance, flame retardant, transparent options available.
Cons: More expensive than other options, susceptible to scratching.
Examples: Safety shields, bulletproof glass, lenses, greenhouses.
5. Nylon:

Pros: Excellent strength, wear resistance, good chemical resistance, self-lubricating.
Cons: More expensive than other options, can absorb moisture and swell.
Examples: Gears, bearings, electrical components, marine hardware.

Remember, this is just a starting point. Consulting with a material engineer or plastics expert is highly recommended to discuss your specific application and identify the most suitable material for your needs. They can help you consider factors like long-term performance, environmental impact, and cost optimization to make the best decision for your project.