Processing equipment fit
Standard injection/extrusion machines; general-purpose screws; standard molds; hot runners work well (low shear)
Polypropylene Overview
Polypropylene is a thermoplastic polymer first commercially produced in the 1950s. It has become the second-most widely produced plastic globally, valued for its balance of mechanical strength, chemical resistance, and low cost. The material belongs to the polyolefin family and exhibits a semi-crystalline, non-polar structure that provides excellent resistance to moisture, fatigue, and most chemical environments.
Polypropylene demonstrates excellent resistance to a broad range of chemicals at room temperature. The material resists non-oxidizing acids including hydrochloric, phosphoric, and sulfuric acid at moderate concentrations. Alkaline solutions, including sodium hydroxide and potassium hydroxide, do not attack polypropylene at typical operating temperatures. Most organic solvents, fats, and oils show little effect on the polymer, making it suitable for chemical storage and laboratory equipment.
The material resists biological attack, remaining stable when exposed to bacteria, fungi, and most biological fluids. This resistance supports medical and pharmaceutical applications where sterilization and biological compatibility are required.
Strong oxidizing agents pose the primary chemical limitation. Concentrated nitric acid, hydrogen peroxide at elevated concentrations, and halogenated solvents can degrade polypropylene. At elevated temperatures, nonpolar solvents such as xylene, toluene, and decalin can dissolve the polymer, limiting high-temperature chemical resistance. Aromatic hydrocarbons and chlorinated solvents should be avoided in polypropylene applications.
Performance Characteristics
Tensile strength
~25–50 MPa
Tensile modulus (Young’s)
~1,100–1,800 MPa (unfilled)
Flexural strength
~35–80 MPa (unfilled)
Flexural modulus
~1,200–1,800 MPa (unfilled)
Elongation at break
~50–700%
Notched Izod impact
~2–10 kJ/m² (unfilled)
Fatigue / endurance
1M cyc
Creep / stress relaxation
Moderate
Continuous use temperature
~80–100 °C (unfilled)
Heat deflection temperature
~50–110 °C at 1.8 MPa (unfilled)
Glass transition temperature (Tg)
−10 to 0 °C (amorphous)
Melting temperature
~130–170 °C
Coefficient of thermal expansion
~8–15 × 10⁻⁵ /K (unfilled)
Thermal conductivity
~0.1–0.25 W/m·K
Water absorption
<0.03% in 24 h
Chemical resistance summary
Very good resistance to water, aqueous salts, most aliphatic hydrocarbons, oils and fuels; poor against strong oxidizing acids, halogenated hydrocarbons, and aromatic solvents at elevated temperature.
UV/weatherability rating
Poor to fair without stabilizers
Hydrolysis resistance
Excellent
Stress cracking sensitivity
Generally low
Dielectric strength
20–40 kV/mm
Dielectric constant
~2.1–2.3 at 0.1–1 MHz.
Volume resistivity
≥10¹⁵ Ω·cm
Surface resistivity
≥10¹³–10¹⁵ Ω/sq
ESD/antistatic behavior
Base PP is insulating; can reach surface resistivity in the ~10⁶–10¹¹ Ω/sq range with additives
UL 94 class
HB / V2 / V0
Glow wire / other fire tests
FR grades 750–960 °C glow wire requirements
Smoke/toxicity
PP combustion mainly yields CO₂, CO, water, and soot; smoke/toxicity strongly influenced by FR or additive package
Coefficient of friction
~0.25–0.35 static, ~0.2–0.3 dynamic for unfilled PP.
Wear resistance / bearing suitability
Good abrasion resistance and low friction versus many plastics, suitable for lightload, lowspeed bearings and sliding elements; performance improves further in filled/modified “bearing grade” PP compounds
Strengths, Weaknesses & Operating Limits
Key Strengths
- Low Density and Light Weight: The low specific gravity enables weight reduction in automotive and consumer products, reducing material costs and shipping expenses while maintaining adequate mechanical performance.
- Chemical Resistance: Broad resistance to acids, bases, and solvents supports chemical processing equipment, laboratory ware, and pharmaceutical packaging applications.
- Fatigue Resistance: Exceptional performance under repeated flexing enables living hinge designs and applications requiring millions of flex cycles without failure.
- Moisture Resistance: Negligible water absorption maintains dimensional stability and eliminates the need for drying before processing.
- Cost Effectiveness: Polypropylene ranks among the most economical engineering thermoplastics, offering an attractive balance of properties and price for high-volume applications.
- Processability: The material processes easily through injection molding, extrusion, blow molding, and thermoforming, with fast cycle times and minimal scrap generation.
Known Weaknesses
- UV Degradation: Unprotected polypropylene degrades rapidly under sunlight exposure. UV stabilizers are required for outdoor applications.
- Low Temperature Brittleness: Impact strength decreases significantly below 0°C, limiting winter outdoor use unless impact-modified grades are specified.
- Limited High Temperature Performance: Heat deflection temperatures restrict use in high-temperature structural applications compared to engineering thermoplastics like nylon or polycarbonate.
- Oxidation Susceptibility: Strong oxidizing chemicals and prolonged thermal exposure can cause property degradation. Antioxidant stabilizers extend service life.
- High Thermal Expansion: Significant dimensional changes across temperature ranges require careful design consideration in precision assemblies.
- Bonding Challenges: The low surface energy of polypropylene makes adhesive bonding difficult. Surface treatments or mechanical fastening are typically required for assembly.
Operating limits
- Operating temperature envelope: roughly −20 to 80–100 °C for continuous use; highheat/reinforced grades can reach ~110–120 °C continuous, shortterm higher.
- Load/time limits: for longterm static loading (≈10,000 h), design stresses are usually kept to a small fraction of tensile strength, on the order of a few MPa, strongly grade and temperaturedependent
- Processing constraints: generally no drying needed; melt window ~200–260 °C; semi‑crystalline shrinkage makes it warpage-prone in thick/uneven sections; sensitive to over-heating and long residence times (oxidative degradation).
Design, Assembly & Aesthetics
Surface finish capability: Medium gloss; replicates fine textures well; shows weld lines and flow marks
Sink/warpage/visible defects tendency: Prone to sink marks and warpage due to high shrinkage; worse in thick sections
Colorability: All colors achievable via masterbatch; bright/dark good, white excellent; typically opaque, some translucency in thin copolymer
Color stability: Fair; UV stabilizers needed to prevent yellowing/chalking; heat can cause discoloration if overheated
Optical properties: Opaque (semi-crystalline); high haze even in thin sections; refractive index ~1.49
Scratch/chemical mar resistance notes: Fair scratch resistance; good against mild chemicals/oils, poor vs. solvents/aromatics
Marking methods: Pad print, inkjet, hot stamping good; laser marking possible on filled grades; embossing clean.
Coating/painting/plating suitability: Paintable with pretreatment (flame/plasma); plating rare, needs special adhesion promoter
Joining methods: Ultrasonic/vibration welding excellent; laser welding good on compatible grades; adhesives fair (surface prep needed); clean joints possible
Featured
Suppliers and Products
Omnipro®
View Products
Verity™
View Products
Ineos®
View Products
Invista™
View Products
Hifax®
View Products
Hostacom®
View Products
Metocene®
View Products
Pro-fax®
View Products
Softell®
View Products
Pinnacle™
View Products
Geon
View Products
PureFive™
View ProductsFrequently Asked Questions
Polypropylene is a thermoplastic polymer produced through the polymerization of propylene monomers using catalysts. The stereospecific polymerization process, developed by Giulio Natta in the 1950s, creates isotactic polypropylene with regular molecular structure and semicrystalline morphology. Modern production uses Ziegler-Natta or metallocene catalysts in continuous polymerization reactors operating at controlled temperature and pressure conditions.
Homopolymer polypropylene contains only propylene monomers, providing maximum stiffness and heat resistance. Random copolymers incorporate small amounts of ethylene distributed randomly along the polymer chain, improving clarity and low-temperature impact. Block copolymers contain segments of polypropylene alternating with ethylene-propylene rubber, delivering enhanced impact strength while maintaining reasonable stiffness.
Food-grade polypropylene meets FDA requirements for food contact applications and is widely used in food packaging, containers, and food service items. The material does not leach harmful substances under normal use conditions and withstands microwave heating and dishwasher temperatures. Specific grades are formulated and tested for food contact compliance.
Polypropylene offers higher stiffness, better heat resistance, and superior chemical resistance compared to polyethylene. The material's higher melting point enables steam sterilization and hot-fill applications where polyethylene would deform. Polypropylene is lighter than polyethylene and provides better fatigue resistance for living hinge applications. Polyethylene offers better low-temperature toughness and lower cost for less demanding applications.
Polypropylene is recyclable and carries recycling code 5. Post-consumer recycled material finds applications in automotive parts, industrial products, and non-food packaging. Recycling requires sorting, cleaning, and reprocessing through extrusion or compounding. Material properties may degrade slightly through recycling, but proper processing maintains acceptable performance for many applications.
Connect with Our Experts Today
If you need some extra guidance in finding the right product, fill out the form and our team will be in touch shortly.
Contact UsBrowse and Order Products on Formerra+
Explore Our Products on Formerra+ Discover the full range of high-quality products on the upgraded Formerra+ online experience.
Visit Formerra+Sources
BMP Medical. "Best Types of Plastic for Medical Equipment or Devices." June 2025. https://bmpmedical.com/what-plastics-are-used-in-medical-devices/
Braskem S.A. "Polypropylene Chemical Resistance." Technical Literature, December 2005. https://www.braskem.com.br/Portal/Principal/Arquivos/html/boletm_tecnico/PP%20Chemical%20Resistance.pdf
Engineering ToolBox. "PP Polypropylene - Chemical Resistance." April 2024. https://www.engineeringtoolbox.com/polypropylene-pp-chemical-resistance-d_435.html
International Polymer Solutions. "Polypropylene Typical Properties." Technical Bulletin. https://www.ipolymer.com/pdf/Polypropylene.pdf
MatWeb. "Heat Deflection Temperature Testing of Plastics." Material Property Data. https://www.matweb.com/reference/deflection-temperature.aspx
Palmetto Industries – Polypropylene Properties (https://www.palmetto-industries.com/polypropylene-properties/)
PMC - PubMed Central. "Research and application of polypropylene: a review." https://pmc.ncbi.nlm.nih.gov/articles/PMC10761633/
Protolabs. "Polypropylene (PP): Understand the Key Benefits and Applications." Materials Guide. https://www.protolabs.com/materials/polypropylene/
SpecialChem – Polypropylene Guide (https://www.specialchem.com/plastics/guide/polypropylene-pp-plastic)
SyBridge Technologies. "Know Your Materials: Polypropylene (PP)." https://sybridge.com/know-your-materials-polypropylene/