Both materials do the same job on the drawing. They behave very differently on the line, and the difference shows up two years later in the field. Here is what actually separates them, and four rules for picking one.
Two families, one job
A sleeve is a thin-walled moulded part, and the material has to deliver three things at once: enough stiffness to hold shape during handling, enough elasticity to grip the wire, and enough chemical stability to survive the environment. PVC and silicone divide those three requirements very differently, which is why the choice is rarely about price alone.
What PVC is good at
- Dimensional stability. PVC moulds to a sharp, repeatable edge and holds its shape, so bore and length vary less from part to part. On automated insertion equipment this is the difference between a stable cycle and constant jams.
- Clean appearance. Gloss or matte finishes are easy to control, colour is consistent across batches, and the part looks the same after a year on the shelf.
- Transparent grades. Clear PVC lets an inspector see the crimp through the sleeve — useful on terminals where a visual pull test is part of the inspection plan.
- Cost. Material and cycle time are both lower than silicone at the same volume, and general-purpose grades need no special handling.
What PVC is not good at
PVC is stiff. It tolerates one installation and then stays where it was put. Bend it repeatedly, or force it over an oversized terminal, and it whitens at the stress line and eventually cracks. It also stiffens further in cold conditions, which is where most winter-time split reports come from. General-purpose PVC compounds also have a narrower useful temperature band than silicone; the exact rating depends on the compound, so always work from the compound datasheet rather than from a rule of thumb.
What silicone is good at
- Elastic range. Silicone stretches far and returns, which means one part can cover a range of terminal and wire combinations, and a sleeve can be pushed over a flange without splitting.
- Flex after assembly. Where a wire leaves a terminal at an angle and then moves — engine bays, handheld tools, moving machine parts — silicone absorbs the bend instead of concentrating it.
- Temperature headroom. Silicone rubber generally tolerates a wider service temperature range than general-purpose PVC. Do not treat that as a licence to skip the datasheet: the usable range depends on the specific compound and on whether the part is under load.
- Compression set. Silicone keeps pushing back after long compression, so a grip that depends on tail tension stays tight rather than relaxing.
What silicone is not good at
It is soft, so thin walls tear at a sharp moulded edge, and it picks up dust and swarf in a machine shop faster than PVC. Its tear strength is lower, which matters on parts with thin flanges or small slots. Colour matching across batches is harder to hold than on PVC. And it costs more — both material and cycle time — so specifying silicone for a part that is installed once and never touched is money spent on nothing.
Side-by-side
| Criterion | PVC | Silicone |
|---|---|---|
| Flexibility after assembly | Low — one install, then set | High — repeated bending tolerated |
| Holds moulded shape | Excellent | Good, but softer edges |
| Temperature range | Narrower; compound dependent | Wider; compound dependent |
| Oil and fuel contact | Fair to poor on general grades | Better on many compounds; verify per application |
| Transparent option | Yes, common | Possible but less common |
| Colour consistency | Very good | Good |
| Tear strength | Good | Lower — thin walls need care |
| Relative cost | Lower | Higher |
| Best fit | Fixed wiring, cabinets, high volume | Moving wires, heat, tight bends |
Four rules that settle most decisions
- If the wire moves after assembly, specify silicone. Repeated flexing is the one thing PVC cannot do, and no amount of wall thickness fixes it.
- If the sleeve is installed once inside a cabinet or a control box, specify PVC. You get better tolerances and lower cost for the same protection.
- If the assembly sees heat or cold outside the comfortable band, ask for the compound datasheet for both options before deciding. A “high temperature PVC” is a different product from general-purpose PVC, not a marketing label.
- If you need to see the crimp, specify clear PVC first. Transparency is a genuine inspection aid and is hard to match in silicone.
When the answer is neither, or both
Two cases break the binary. The first is appearance-driven parts — tool grips and covers — where a soft, high-grip compound matters more than either base polymer; those are specified by hardness and surface texture, not by PVC-versus-silicone. The second is a single series supplied in both materials: several of our terminal sleeve ranges are moulded in PVC for the standard build and in silicone for the high-flex variant, using the same tooling. That is often the practical answer — one geometry, two materials, so the design does not change when the application does.
What to confirm with a supplier
Ask for the compound identification, the hardness in Shore A, and a declaration covering RoHS and REACH for the specific grade being quoted — not for the polymer family in general. Ask whether the quoted grade is the same one used for the sample, because substitutions at the compounding stage are common and invisible until a part fails. And ask what the supplier's incoming check covers: bore, length, wall thickness and hardness are the four measurements that predict field behaviour.