Which material for industrial caps and plugs

Which polymer should you choose for an industrial plug or cap? It depends on what function the component needs to perform. These are the most common pairings:

thread protection → LDPE for basic applications, TPE for heavy-duty use, nylon where impact and pressure are involved
contamination prevention → LDPE in standard environments, HDPE under mechanical stress, EPDM across wide temperature ranges
masking and treatments → high-temperature vinyl, EPDM, silicone up to 315 °C
handling and transport → LDPE for standard environments, TPE for impact and abrasion, PVC for long-distance transport

Then, check the pairing against five critical parameters: operating temperature, chemicals in contact with the component, sealing requirements, resistance to impact and shearing, and installation/removal method. Choosing the wrong material is not merely an aesthetic issue: it can compromise system cleanliness, deform parts, damage threads, and disrupt assembly and treatment processes.

Contents

Why the material matters as much as the component
Which material for thread protection
Which material for contamination prevention
Which material for masking
Which material for handling, transport and storage
The 5 factors that guide material selection
Assessment questions to ask before ordering
Physical properties matrix for polymers
Chemical resistance: which polymer withstands which substance
Beyond the material: shape, installation and ergonomics
Frequently asked questions

Why the material matters as much as the component

Caps and plugs play an essential role throughout the product lifecycle. They protect connections, withstand damage on the production line, mask critical areas during painting and treatment processes, prevent contamination, facilitate handling and storage, and retain residual fluids.

Each function helps eliminate potential costs later in the product lifecycle: rework, re-machining a thread, a rejected batch, or production downtime. In hydraulic and pneumatic systems, where leak-tight seals, high pressures and precision couplings are involved, there is almost no room for approximation. The material is therefore part of the technical specification, rather than just an accessory listed in a catalogue.

Which material for thread protection

The thread is the most expensive part to rework and the most exposed during assembly, storage, transport and maintenance. The material must withstand shearing (the detachment of fragments on sharp profiles), impact and the ingress of particles.

These requirements lead to 3 recurring configurations, in increasing order of performance:

Basic level, LDPE – prevents contamination and dust, high chemical resistance, low impact resistance.
Intermediate level, TPE – adds resistance to shearing and impact, with excellent chemical resistance.
Premium level, nylon – high impact and tensile strength, strong resistance to shearing, withstands pressure, but only partial chemical resistance.

In all three cases, if an effective fluid seal is required, a gasket or O-ring must be added: the plug alone protects, but does not seal.

If your application involves threaded profiles, you can find a dedicated comparison in our article on types of thread caps and the full range in the thread protection and threaded plugs section.

Which material for contamination prevention

The goal here is to prevent particles from entering during assembly, storage, transport and maintenance, while ensuring suitable thermal tolerance for the working environment. There are three reference materials:

Basic level, LDPE – suitable for standard environments, high chemical resistance, low impact resistance.
Intermediate level, HDPE – performs the same function with greater impact resistance and excellent chemical resistance.
Premium level, EPDM – wide temperature range, good impact resistance, sealing at low pressures, excellent chemical resistance.

Which material for masking

In masking applications, the material must withstand oven temperatures and harsh chemicals, remain suitable for sandblasting, anodising or plating, and be removed cleanly without leaving residue.

Three materials can withstand these conditions, in increasing order of overall performance:

Basic level, high-temperature vinyl – up to 218 °C, excellent chemical resistance, available in cap form.
Intermediate level, EPDM – up to 177 °C, excellent chemical resistance, suitable for all masking processes.
Premium level, silicone – up to 315 °C, excellent chemical resistance, the required choice for the most severe thermal cycles.

To understand how material, geometry and the painting cycle work together, see our guide on how to choose the best caps for painting and masking processes.

Which material for handling, transport and storage

Here the key factors are impact, abrasion, humidity and duration of exposure. For long-distance transport, higher-density materials provide greater protection.

Basic level, LDPE – low density, good chemical resistance, protection from dust, poor UV resistance.
Intermediate level, TPE – good impact and abrasion resistance, excellent weather resistance, flexible and recyclable, remains securely in place.
Premium level, PVC – excellent impact and abrasion resistance, higher density, excellent chemical resistance and resistance to operating temperatures.

The 5 factors that guide material selection

The pairings described so far cover most cases, but they do not replace the need for verification under actual application conditions. Before confirming a product code, it is advisable to define the operating context.

The factors that matter most are:

application – does the plug protect, mask, seal, or is it used only for transport?
environment – UV exposure, humidity, salt spray, temperature fluctuations, partial or total immersion
production process – oven cycles, sandblasting, anodising, plating, powder coating
sustainability – need for recycled materials, end-of-life recyclability, reuse over multiple cycles
ergonomics – manual or automated installation and removal, use of tools, colour coding.

Assessment questions to ask before ordering

This checklist covers the variables that determine compatibility between the material and the application. Answering these questions can dramatically shorten the selection process.

Area	Key questions
Temperature	What are the minimum and maximum ranges? Direct or indirect heat? Are the changes rapid?
Chemical resistance	Which substances are in contact with the component? Solvents or corrosive agents? For how long?
Humidity and weathering	Is UV resistance required? Does the component come into contact with residual fluids? Is immersion expected?
Sealing	Is an effective seal required? How and at what stage will it be removed?
Tensile strength, impact and rigidity	Can impacts or operating conditions deform the part? Single-use or multi-use application?
Shear and torque	Is there a risk of material shearing or fragments detaching on threads and rotating parts?
Pressure tolerance	What pressure value in bar or PSI? How long does the component remain under pressure?
Installation and removal	Manual or automated operation? Are tools required? Is colour coding required?
Sustainability	Are recycled polymers required? Will the component be recovered or reused?

Physical properties matrix for polymers

This matrix is useful for checking the selected pairing or assessing alternatives. It compares the polymers most commonly used for industrial caps and plugs across 5 physical properties. Temperature values are indicative and should be checked against the technical data sheet of the specific product.

Material	Chemical resistance	Weathering	Temperature range	Shear resistance	Oils and greases
LDPE (low-density polyethylene)	Excellent	Poor UV resistance	-50 °C to 79 °C	Fair	Moderate
HDPE (high-density polyethylene)	Excellent	Poor UV resistance	-50 °C to 60 °C	Good	Moderate
PP (polypropylene)	Very good	Poor UV resistance	-10 °C to 120 °C	Good	Moderate
TPE (thermoplastic elastomer)	Excellent	Excellent	-30 °C to 95 °C	Poor	Excellent
TPR (thermoplastic rubber)	Excellent	Excellent	-30 °C to 95 °C	Poor	Good
Vinyl / PVC	Very good	Good	-20 °C to 177 °C	Moderate	Good
High-temperature vinyl / PVC	Very good	Good	-20 °C to 218 °C	Moderate	Good
Nylon / PA	Poor	Good UV resistance	-40 °C to 149 °C	Excellent	Excellent
Silicone	Excellent	Excellent with specific modifications	-50 °C to 315 °C	Poor	Poor
EPDM (ethylene propylene diene rubber)	Excellent	Excellent	-50 °C to 177 °C	Fair	Poor

Chemical resistance: which polymer withstands which substance

When the component comes into contact with acids, alkalis or solvents, mechanical retention alone is not enough. This comparison helps rule out incompatible options immediately.

Material	Sunlight	Weak acids	Strong acids	Strong alkalis	Organic solvents
LDPE (low-density polyethylene)	Rapid surface microcracking	Resistant	Attacked by oxidising agents	Resistant	Resistant below 60 °C
HDPE (high-density polyethylene)	Rapid surface microcracking	Highly resistant	Attacked by oxidising agents	Highly resistant	Resistant below 80 °C
PP (polypropylene)	Rapid surface microcracking	No resistance	Attacked by oxidising agents	Highly resistant	Resistant below 80 °C
TPE (thermoplastic elastomer)	Good resistance	Highly resistant	Attacked	Resistant	Poor
TPR (thermoplastic rubber)	Subject to microcracking	Highly resistant	Attacked by oxidising agents	Highly resistant	Resistant to most
Vinyl / PVC	Good resistance	Highly resistant	Resistant	Resistant	Alcohol, aliphatic hydrocarbons and oils
Nylon / PA	Tends to discolour	Discolours	Attacked	No resistance	Resistant to most
Silicone	Highly resistant	Poor	Poor	Poor	Poor
EPDM (ethylene propylene diene rubber)	Highly resistant	Good resistance	Highly resistant	Highly resistant	Resistant

Beyond the material: shape, installation and ergonomics

Once the polymer has been selected, the geometry and the application method still need to be defined. The key aspects to assess at this stage are:

push-fit or screw installation
threaded or non-threaded application
tapered or straight shape, flanged or smooth
calibrated or expandable fit
hexagonal head or round head
compatibility with installation and removal tools
speed of installation and removal on the production line
reusability over multiple cycles
compatibility with O-rings and gaskets

To explore the different plug shapes in more detail, see our guide to the main features of a cap.

Frequently asked questions about choosing materials for caps and plugs

What is the most heat-resistant material for an industrial plug?

Silicone, with an operating range of up to 315 °C. It is followed by high-temperature PVC up to 218 °C and EPDM up to 177 °C. The BMP range of silicone caps covers applications involving severe thermal cycles.

Which material should be used to protect a thread from impacts and deformation?

Nylon, thanks to its high resistance to impact, tensile stress and material shearing. However, its chemical resistance is limited, so it should be ruled out in the presence of strong acids or alkalis.

Does a plastic plug provide a leak-tight seal?

No, not on its own. To achieve an effective seal on fluids or gases, it must be combined with a gasket or O-ring sized for the application.

Can polyethylene withstand prolonged outdoor exposure?

LDPE and HDPE rapidly develop surface microcracking under sunlight. For prolonged UV exposure, EPDM, silicone or PVC are more suitable.

How can you check whether a material is compatible with your application?

By testing a sample: the component is tested under the actual temperature, pressure and chemical-contact conditions before confirming the supply.

Need help choosing?

BMP TAPPI manufactures plastic plugs, caps, covers and components for industrial applications. If you have a drawing, a specification or simply an application problem to solve, our technical department will support you in selecting the material and, when the standard catalogue is not enough, in developing a dedicated component.

News

Materials for caps and plugs: which polymer for each application