Polypropylene (PP) vs LDPE
Polypropylene (PP) and LDPE are both low-cost, chemically inert commodity polyolefins, but they differ in stiffness, temperature range, and flexibility. PP is stiffer, tolerates higher heat, and resists fatigue well enough for living hinges. LDPE is softer and far more flexible, ideal for film, bags, and squeeze parts. Both rate top-tier for chemical resistance and share the lowest cost tier.
The verdict
Choose Polypropylene for stiffer parts, higher service temperature, and repeated flexing such as living hinges. Choose LDPE when you need a soft, highly flexible material for film, liners, and squeezable parts. Both are cheap and chemically inert; PP is the structural polyolefin, LDPE the flexible one.
Side-by-side data
| Property | Polypropylene (PP) | LDPE |
|---|---|---|
| Category | Plastic | Plastic |
| Density (g/cm³) | 0.91 | 0.92 |
| Tensile strength (MPa) | 35 | 12 |
| Yield strength (MPa) | 32 | 10 |
| Elongation (%) | 100 | 400 |
| Hardness | R90 | 45 Shore D |
| Max service temp (°C) | 100 | 60 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 0.12 | 0.33 |
| Typically used for | Living hinges & chemical containers | Flexible film, bags & liners |
Which should you choose?
Choose Polypropylene (PP) when…
- You need stiffness and form-holding — tensile ~35 MPa vs LDPE's ~12 MPa (nominal)
- Living hinges or repeatedly flexed features are required; PP's fatigue resistance is its signature strength
- Service runs warmer, up to ~100 C versus LDPE's ~60 C
- Chemical containers, closures, and structural housings are the target
- You want a rigid, dimensionally stable wall rather than a floppy one
- Lightweight matters — PP is among the least dense plastics at ~0.91 g/cm3
Choose LDPE when…
- Flexibility and softness are the goal — LDPE elongates ~400% and is far more pliable
- You are making film, bags, liners, or squeeze bottles
- A soft, low-hardness surface (~45 Shore D) suits the part better than rigid PP
- Service stays cool — LDPE tops out around ~60 C
- Excellent chemical and moisture resistance is needed in a flexible form (5/5 corrosion)
- Cost is critical; LDPE shares the lowest cost tier (~1.0/5)
Key differences that matter
- Both are inexpensive (~1.0/5 cost) and rate 5/5 for chemical resistance
- PP is markedly stiffer and stronger (~35 MPa vs ~12 MPa tensile)
- LDPE is far more flexible, with ~400% elongation and a soft, low-modulus feel
- PP tolerates more heat (~100 C vs ~60 C max service)
- PP resists fatigue well, enabling living hinges that survive thousands of flex cycles
- Both are very low density (PP ~0.91, LDPE ~0.92 g/cm3) and float in water
- LDPE machines poorly (2.5/5) and is almost always formed or extruded rather than machined
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Why is PP used for living hinges and not LDPE?
Polypropylene has excellent flex-fatigue resistance, so a thin PP hinge can bend hundreds of thousands of times without cracking. LDPE is flexible but lacks the same fatigue endurance and is too soft to provide the snap and rigidity a hinged closure needs. PP's combination of stiffness plus fatigue life makes it the living-hinge standard.
Which is more flexible, PP or LDPE?
LDPE, by a wide margin. It elongates around 400% and has a soft, low-modulus character that makes it ideal for film, bags, tubing, and squeeze bottles. PP is comparatively rigid. If your part needs to bend, stretch, or compress softly and repeatedly without holding shape, LDPE is the better fit.
Which handles higher temperatures?
Polypropylene. This dataset lists PP service near 100 C versus LDPE around 60 C. PP can survive dishwasher and short hot-fill cycles where LDPE would soften or distort. For any warm or hot application, PP gives meaningful margin; LDPE should be kept to ambient or cool service.
Are both chemically resistant?
Yes — both rate 5/5 for corrosion resistance and are inert to most acids, bases, and aqueous solutions, which is why both appear in chemical containers and liners. Differences come down to mechanical form: PP for rigid chemical tanks and closures, LDPE for flexible liners, films, and squeeze containers.
Which is cheaper?
They are essentially tied at the lowest cost tier (~1.0/5 each). Cost rarely decides between them; the choice is driven by mechanical needs. Pick PP for stiffness, heat, and hinges; pick LDPE for flexibility and film. Both are among the most economical thermoplastics available.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.