Temperature versatility
This is a typical reason for selecting suitable grades. Check the manufacturer’s data sheet for the actual formulation and service conditions.
ENGINEERING PLASTICS
SI(Silicone rubber)
A flexible material based on a silicon-oxygen backbone, rather than the carbon backbone of many everyday plastics.
Rubber / elastomer
THE NAME, EXPLAINED
What is SI?
SI means Silicone rubber.
A flexible material based on a silicon-oxygen backbone, rather than the carbon backbone of many everyday plastics.
Worth knowing
SI is a reference-list label; silicone rubber is also commonly marked VMQ. Cured silicone needs a specialist route, not normal melt recycling.
WHY MANUFACTURERS CHOOSE IT01 02 03
Properties with a practical purpose.
Elasticity
The ability to deform and recover some or all of the original shape.
Grade-dependent sealing performance
This is a typical reason for selecting suitable grades. Check the manufacturer’s data sheet for the actual formulation and service conditions.
Properties vary with formulation, reinforcement, moisture, processing and service conditions. Use the exact grade data sheet for engineering decisions.
THE NEXT-CYCLE QUESTION
What matters when considering recovery?
Finished rubber is commonly cured. A rubber-specific route is needed rather than assuming standard melt recycling.
SI is a reference-list label; silicone rubber is also commonly marked VMQ. Cured silicone needs a specialist route, not normal melt recycling.
Poly-Cycle can discuss your material information and collection requirements. Inclusion in this guide does not confirm acceptance, a particular recycling method or that every operation takes place at a Poly-Cycle facility.
How assessment and collection workMake the enquiry easier
- Confirm the identity. Keep the manufacturer, trade grade and polymer marking. For an additive or chemical, include the safety data sheet.
- Describe the batch. Give the weight, colour and form: pellets, parts, sheet, film, fibre or another format.
- Explain what else is present. Declare fillers, coatings, metal inserts, other polymers and previous contact with chemicals or other contaminants.
- Agree the route. Share photographs and your collection postcode before arranging a movement.
FROM THE GUIDE TO YOUR MATERIAL
Have SI to discuss?
Send the team your grade details, approximate quantity and photographs. We can discuss the information needed for your particular batch.
KEEP EXPLORING
Browse Engineering Plastics Related material guides.
PA
Polyamide (nylon)
A family of tough plastics used for parts that rub, flex or carry a load. Nylon is the familiar name for many polyamides.
Understand this material PA 4.6Polyamide 4,6 (nylon 4,6)
A nylon grade chosen for demanding components that need to retain stiffness when warm.
Understand this material PA 6Polyamide 6 (nylon 6)
A widely used nylon for durable moulded components and fibres.
Understand this materialTechnical references and reading
General material information reviewed 1 November 2026. Manufacturer information supports the material descriptions; recycling enquiry guidance is an editorial synthesis, not a statement of a supplier’s or Poly-Cycle’s acceptance criteria.
Browse this guide under: Engineering Plastics. The original category inventory was informed by RM Group’s plastics directory; explanations have been written for Poly-Cycle.