PP Vs PE Plastics: Key Differences Explained

What Are These Plastics?

Polypropylene (PP) and Polyethylene (PE) are big plastic types we see a lot. They make things we use each day.

PP is made from stuff called C3H6. PE is made from C2H4. That may sound big, but it just means they are made from different building blocks.

These plastics can be hard or soft. It all depends on how they are made.

Types You Should Know

PP comes in two main types:

Homopolymer (very stiff)
Copolymer (less stiff but stronger)

PE has three main types:

HDPE (High Density PE) – for milk jugs and pipes
LDPE (Low Density PE) – for plastic bags
LLDPE (Linear Low Density PE) – for food wrap

Let’s look at a that works with these materials.

Big Differences in How They Work

What to Compare	Polypropylene (PP)	Polyethylene (PE)
How Heavy	0.9 g/cm³	HDPE: 0.91–0.96 g/cm³LDPE: lighter
Melting Point	160°C (hot!)	HDPE: 120–130°CLDPE: 105–115°C
How Strong	25–35 MPa	HDPE: 18–31 MPaLDPE: 8–15 MPa
Cost	$1.50–$2.00 per kg	HDPE: $1.00–$1.50 per kgLDPE: $0.80–$1.20 per kg
Recycling Code	#5 (only 3% recycled)	HDPE: #2 (30% recycled)LDPE: #4 (6% recycled)

PP can get very hot without melting. This makes it good for things that go in the microwave or dishwasher.

PE is often cheaper than PP. This is why we see it in so many bags and bottles.

What Happens With Chemicals

PP is good with:

Many cleaning soaps
Most oils

But not good with:

Chlorine (like in pool water)
Strong acids

PE is good with:

Acids
Many chemicals in your home

But not good with:

Car oil
Gas

If you want to make custom parts with these plastics, check out CNC polypropylene machining services.

Where We Use These Plastics

Places PP Works Best

Cars: PP makes car bumpers and parts inside your car.
Medical Stuff: Things like syringes use PP because it can be very clean.
Food Containers: The ones that say “microwave safe” are often PP.
Pipes: Some pipes that carry hot water.

Places PE Works Best

Bags: Most shopping bags are LDPE.
Bottles: Milk jugs and shampoo bottles use HDPE.
Toys: Many plastic toys are PE.
Pipes: HDPE makes pipes that won’t rust.

A real world example: HDPE pipes can hold water with 100 PSI pressure, which is more than PP pipes can take.

For projects using PE, many turn to specialized HDPE CNC machining services.

Which One Costs Less?

PE usually costs less than PP:

PE: $0.80-$1.50 per kg
PP: $1.50-$2.00 per kg (about 30% more)

This is a big reason why so many bags and simple bottles use PE. When companies make lots of things, saving a bit on each one adds up to big money!

Which is Better for the Earth?

Both plastics can be recycled, but there’s a big difference in how much actually gets recycled:

HDPE (milk jugs): About 30% gets recycled
PP (food containers): Only about 3% gets recycled

Milk jugs made from HDPE have the best recycling rate of all plastics at about 40%.

Both plastics stay in landfills for a very long time (hundreds of years).

How to Pick the Right One

Ask these questions to pick the right plastic:

Will it get hot?
- If yes, pick PP (can take up to 160°C)
- If no, either works (but PE might be cheaper)
Will it touch chemicals?
- For acids, pick PE
- For solvents, pick PP
Need it to bend a lot?
- For very bendy things like bags, pick LDPE
- For stiff things that need a hinge, pick PP
On a tight budget?
- PE is usually cheaper

Real World Examples

Case Study: In landfills, HDPE sheets (called geomembranes) are used to stop toxic stuff from leaking into the ground. They’re used in 90% of landfill projects because they resist so many chemicals.

Case Study: PP is used in car parts that need to last a long time and handle heat from the engine.

Questions People Often Ask

Which is stronger, PP or PE?

PP is usually stronger and stiffer. This makes it good for things that need to hold their shape. HDPE comes close, but LDPE is much less strong.

Can PP and PE be recycled together?

No! They have different melting points. They need to be sorted and recycled separately.

Is PP safe for food?

Yes! PP is very safe for food. This is why it’s used for food containers that go in the microwave.

Which is better for outside use?

HDPE is better for long-term outside use. It handles sun and rain better than PP.

Wrap-Up: Which Should You Pick?

Pick PP when you need something that:
- Handles high heat (like microwaves)
- Needs to be stiff but still bend (like a hinge)
- Must be very clean (like medical items)
Pick PE when you need something that:
- Needs to be very cheap
- Must touch acids or chemicals
- Needs to be very flexible (LDPE)
- Will be outside for a long time

Bot materials have their special jobs. The best one depends on what you need it to do!