Use rubber extrusion for parts with one constant cross-section made in lengths, such as seals, strips, cord, tube and edge trim. Use rubber moulding for parts with a 3D shape, a closed form, varying thickness or metal inserts, such as grommets, bellows, bushes and buffers. Seal frames often use both: extruded lengths joined with moulded corners. Walker Rubber extrudes and moulds in-house, so it can recommend the best route for your part.
Not sure which process suits your part? Send us the drawing and we’ll tell you.
What is rubber extrusion?
Rubber extrusion forces uncured rubber through a shaped steel die to make a continuous length with a constant cross-section. The length is then vulcanised (cured) to set its shape and properties. Walker Rubber extrudes lengths from 1 m to 10,000 m.
What is rubber moulding?
Rubber moulding forms rubber inside a closed, heated mould tool, where it cures into the final 3D shape. The three main methods are compression, transfer and injection moulding. See Moulding Rubber Parts for how each works.
Extrusion vs moulding: how do they compare?
Factor | Extrusion | Moulding |
Part shape | Constant cross-section, any length | Any 3D shape, closed forms, varying thickness |
Tooling | Extrusion die: lower cost, typically 2–3 weeks in-house | Mould tool: higher cost, more complex |
Cost per metre or per part | Low for long lengths | Low per part at volume; higher for short runs |
Volumes | 1 m to 10,000 m; no MOQ on standard compounds once tooling exists | Prototypes to high volume; process chosen by volume |
Tolerances (ISO 3302-1) | Classes E1–E3 | Classes M1–M4, generally tighter |
Metal inserts | Not possible in-line (can be bonded afterwards) | Moulded in during transfer or compression moulding |
Typical parts | Door and window seals, gaskets strip, cord, tube, edge trim | Grommets, bellows, bushes, dust covers, buffers |
How do I decide?
- Does the shape stay the same along its length? If yes, extrude it. If no, mould it.
- Is it a closed ring or frame? Small rings are usually moulded. Large frames are usually extruded, then joined.
- Does it need a metal insert or bonded plate? Mould it, or bond it after extrusion.
- How many do you need? For low volumes of a simple ring, a joined extrusion may avoid the cost of a mould tool.
- How tight are the tolerances? Moulding generally holds tighter dimensions than extrusion.
Can extrusion and moulding be combined?
Yes. This is often the cheapest way to make a large sealed frame.
- Vulcanised joints (splicing): extruded lengths are cut and joined into rings or frames.
- Moulded corners: the straight runs are extruded, and the corners are moulded onto them in the same compound. Container door seals and window seals are made this way.
- Post-extrusion processing: punching, drilling, notching, printing and riveting add features that would otherwise need a mould.
What does each process cost to set up?
An extrusion die is usually the lower tooling cost, because it only defines a 2D cross-section. A mould tool defines the whole 3D part and may have several cavities. Both are one-off costs held for your repeat orders.
How does Walker Rubber compare?
| Walker Rubber | Single-process supplier |
Processes | Extrusion, compression, transfer and injection moulding, bonding | Usually one |
Process advice | Recommends the lower-cost route for your part | Quotes what it makes |
Tooling | Dies and mould tools made in-house | Often outsourced |
Combined parts | Extrusions with moulded corners and joints | Two suppliers needed |
Frequently asked questions
What is the difference between rubber extrusion and moulding?
Extrusion makes continuous lengths with one cross-section by pushing rubber through a die. Moulding makes 3D parts by curing rubber inside a closed tool.
Which is cheaper, extrusion or moulding?
For long seals and strips, extrusion is cheaper, because the die costs less and the process is continuous. For small 3D parts at volume, moulding is cheaper per part.
Can an extrusion be made into a ring?
Yes. Extruded lengths can be cut and joined into rings and frames, or given moulded corners.
Which process gives tighter tolerances?
Moulding generally does. Moulded rubber is toleranced to ISO 3302-1 classes M1–M4, and extrusions to E1–E3.
Is rubber extrusion a continuous process?
Yes, for screw extruders. The profile is pushed out continuously and cured in-line or in an autoclave, then cut to length.
Can you mould a metal insert into a rubber part?
Yes. Transfer and compression moulding hold the insert in place while the rubber is moulded and bonded around it.
Let us choose the process for you
Send us your drawing or sample, and we’ll recommend extrusion, moulding or a combination.