LDPE vs HDPE

Investigating materials for a design

Despite both materials deriving from polyethylene, differing chemical structures mean Low-Density Polyethylene (LDPE) and High-Density Polyethylene (HDPE) have their own unique characteristics and properties.

When you’re deciding which thermoplastic might be best for your injection molded part, it’s key that you understand the key differences between the two materials.

To help make your decision-making process hassle free, we’ve put together all the information you need to know about LDPE, HDPE and which materials are best for which parts. 

In this article we cover:

  • What is LDPE?

  • What is HDPE?

  • Which material is best for your part?

  • Are HDPE and LDPE more sustainable materials?

So, which is the best material for your injection molded part?

LDPE vs HDPE properties

What is LDPE?

One of the first types of polyethylene to be created, LDPE (low density polyethylene) is produced by putting ethylene gas under high pressure in an autoclave or tubular reactor. This forces the molecules of the monomer to link together into polymer chains. The fact that it’s formed from a gas means that the polymer chains of LDPE branch off from each other. This creates an irregular molecular structure (known as an amorphous structure) which gives LDPE its unique properties.

The characteristics of LDPE

As its name suggests, LDPE is of a lower density than other types of polyethylene. This is thanks to its irregular structure, which leaves plenty of space between molecules and makes LDPE lightweight, transparent and flexible.

This spacious structure also means that the chemical bonds between molecules are relatively weak, this means that LDPE has a relatively low melting point at 115C and is less durable than other types of polyethylene. Despite this, compared to other types of plastic, LDPE is fairly resistant to impact, moisture and other chemicals.

LDPE common characteristics

What is HDPE?

To produce HDPE (high density polyethylene), petroleum is heated to very high temperatures in a process known as ‘cracking’. This turns the petroleum into a gas, these gas molecules then join together to create a raw form of HDPE, this raw material is molded and set into its usable form. This different manufacturing process gives HDPE a regular molecular structure (known as a crystalline structure) with closely connected polymer chains.

The characteristics of HDPE

A tight molecular structure gives HDPE a higher density than other types of polyethylene. The lack of space between molecules also means that the thermoplastic is highly durable, rigid and opaque.

Strong chemical bonds between molecules gives HDPE a higher melting point at 135C and is very strong. It also means that HDPE is inflexible compared to other types of polyethylene, as well as being very resistant to heat, moisture and other chemicals. In fact, HDPE is so resistant that it cannot join to other materials or other HDPE parts very easily.

Which material is best for your part?

Although their molecular structures mean HDPE and LDPE have some material differences, there are some common characteristics between the two, including:

  • Lightweight compared to other thermoplastics.
  • Good level of resistance to impact, chemicals, moisture and weather.
  • Low manufacture and production costs.

These properties mean both LDPE and HDPE can be injected into molds which to make parts that can be used for a huge range of industrial purposes.

Different fits of LDPE and HDPE

Protection parts

The chemical resistance of HDPE and LDPE make them a great option for protection parts, such as spiral wrap hose protectors which have both PP and HDPE parts. Able to resist other chemicals, moisture and weather conditions, HDPE is the material of choice for any parts that require rigidity and strength whereas LDPE is more suitable for protection that requires some flexibility.

Thanks to its semi-rigidity, HDPE is typically used for hydraulic application or pipe protection caps and plugs. Threaded O-ring plugs and protection caps are typically made of HDPE and provide excellent protection from the ingress of dirt, moisture or other foreign objects. Its strength also makes it an appropriate material for some push-to-fit plugs and caps.

However, the flexibility of LDPE makes it ideal for push-to-fit caps and plugs that are easy to apply and remove. Stretch fit cover caps, side release or compression fit plugs made of LDPE are the perfect solution for tricky forms of protection, particularly in pipes or flanges.

Both HDPE and LDPE are used to protect hoses and tubing thanks to their flexibility, impact and abrasion resistance.

Hardware parts

Although LDPE and HDPE are fairly resistant, they don’t provide as much durability as other plastics meaning they’re not often used as the main component of hardware parts. However, they can be used as a component part of feet, castors and gliders alongside nylon or rubber. The qualities of LDPE are ideal for tube inserts and glides, offering secure fitting and covering sharp edges.

Fasteners

Similarly to hardware parts, LDPE and HDPE are not as durable or strong as other plastics and therefore not commonly used in fasteners. The strength and high resistance of nylon means this plastic is more often used in washers, screws and nuts. It’s very rare to find LDPE or HDPE fasteners.

LDPE vs HDPE applications

Are HDPE and LDPE more sustainable materials?

Although both LDPE and HDPE are recyclable, their most common uses mean they're often contaminated with food residues, dirt, or other waste materials, making additional cleaning stages necessary during the recycling process. Despite these challenges, recycling remains the only way to sustainably dispose of these plastics, as neither LDPE nor HDPE is biodegradable.

Like other types of plastic materials, both are made from petroleum-based oil, a non-renewable fossil fuel that makes them fundamentally unsustainable in their current form. However, with ongoing advancements, more sustainable alternatives to LDPE and HDPE plastics are likely to emerge, focusing on reducing environmental impact and promoting circular economy principles.

At Essentra Components, significant investment in state-of-the-art injection molding machinery has allowed nearly all LDPE products to be manufactured with at least 40% recycled plastic content, using a blend of virgin resins and post-consumer resin. This approach ensures the same level of product quality, mechanical integrity, and durability while reducing reliance on virgin plastics.

This initiative is a cornerstone of Essentra Component's ESG strategy and demonstrates its commitment to the Circular Plastics Alliance. With a long-term goal to achieve a minimum of 20% sustainably sourced materials in production, the company is driving efforts toward a more sustainable plastics industry.

Sustainable plastic parts

So, which is the best material for your injection molded part?

Whatever industry you're in—automotive, electronics, manufacturing, medical, consumer goods, packaging, aerospace, or construction—if you're looking for protection or electronic parts, then LDPE (low-density polyethylene) or HDPE (high-density polyethylene) might be suitable options. Both thermoplastic materials have similar fundamental properties, but LDPE offers flexibility, durability, and chemical resistance, whereas HDPE provides rigidity, tensile strength, and impact resistance.

LDPE materials are commonly used for soft-touch components, bottle caps, medical tubing, and flexible containers, while HDPE is ideal for rigid products like hard cases, piping systems, fuel tanks, and industrial trays. Although LDPE or HDPE plastics aren't typically used for hardware parts, bolts, nuts, or fasteners, they are excellent choices if you're looking for sealing solutions, protective coverings, or lightweight electronic components.

Factors like melting point, density, processing temperature, and chemical compatibility often dictate the choice of material. For instance, LDPE injection molding results in a lightweight, flexible product, while HDPE molding produces components with dimensional stability and superior strength.

If you're unsure whether LDPE or HDPE are the most suitable materials for your part, our experts can help. With specialist training, experience in thermoplastic materials, and in-depth knowledge of our product catalog, our team will guide you in identifying the ideal solution. They can assist with queries related to material selection, customization options, polymer grades, and even environmental considerations, ensuring your decision-making process is truly hassle-free and tailored to your application.

Download free CADs and try before you buy

Free CADs are available for most solutions, which you can download. You can also request free samples to make sure you’ve chosen exactly what you need. If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.

Whatever your requirements, you can depend on fast despatch. Request your free samples or download free CADs now.

Questions?

Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.