How to Read a Silicone Rubber Technical Data Sheet Before Approving a Custom Part
A silicone rubber technical data sheet can help a product team narrow a long material list. It cannot, by itself, prove that a finished custom part will fit, seal, stretch, survive cleaning or meet the product’s regulatory obligations. The difference sounds obvious, yet it is one of the most common sources of disagreement during material approval.
The issue is becoming more important as silicone suppliers introduce increasingly specialized grades. For example, DuPont launched its Liveo C6-8XX LSR series on February 3, 2026, highlighting improved rheology, lower viscosity and a 30 to 70 Shore A range for selected healthcare applications. That announcement is useful industry evidence that two materials with a similar hardness can be designed for different processing and application needs. It is not a reason to assume that a new grade is right for every product, or that DX has qualified that specific series. [1]
At DX, we use supplier documentation as the starting point for a material discussion. We then connect it to the part geometry, manufacturing route, application conditions and approval plan. This article explains how brand owners, engineers and purchasing teams can do the same.
A TDS is a screening document not a finished part certificate
Most technical data sheets combine a product description, uncured-material information, cured-rubber properties, test methods, processing guidance and limitations. These categories do different jobs. Viscosity may help a molding team judge flow behavior. Tensile strength may help an engineer compare candidate compounds. A regulatory statement may define what a formulation was designed or tested to support. None of these entries automatically becomes a guaranteed property of every molded component.
One current KCC Silicone LSR product table makes this distinction explicit: its published property data are typical values and should not be used as specifications. The same table also states its laboratory curing condition and shear rate for viscosity. Those details matter because a value without its method and preparation condition is incomplete. [2]
A useful way to read the document is to ask three questions beside every important number:
If the TDS does not answer those questions, treat the number as preliminary selection information. Ask the material supplier or molder for clarification before placing it in a drawing, purchase specification or quality agreement.
Start with the exact grade and revision
“Silicone,” “LSR,” “food grade” and “60 Shore A” are not complete material identities. A useful project record names the supplier, grade, component ratio or catalyst system where relevant, color formulation, and the TDS revision or date reviewed. If pigment, self-lubricating additive, bonding promoter or other modification is added, record that formulation as part of the approved material state.
This prevents an easy purchasing mistake: comparing one supplier’s premium low-compression-set grade with another supplier’s general-purpose grade simply because both are nominally 50 Shore A. It also makes future change control possible. Without a frozen material identity, the team cannot determine whether a later substitution is equivalent to what passed the original trial.
Read the test method before comparing the value
Two data sheets can use the same property name and still report numbers that are not directly comparable. Standards reduce ambiguity, but only when the method, specimen and conditions are aligned.
| TDS field | What it helps screen | What must match for comparison | Finished-part question |
|---|---|---|---|
| Hardness | Feel and indentation stiffness | Durometer type, specimen thickness, timing, temperature and conditioning | Does the actual geometry flex and assemble as intended? |
| Tensile strength and elongation | Strength and stretch of a standard specimen | ASTM or ISO method, specimen shape, extension rate, temperature and cure | Will the part survive its actual stretch and stress concentration? |
| Tear strength | Resistance to propagation from a defined notch or edge | Method and specimen geometry; units; cure and test direction | Are slits, holes, gates or thin edges vulnerable in use or demolding? |
| Compression set | Recovery after a defined compression exposure | Method, specimen, compression, time, temperature and recovery interval | Will the assembled seal retain function after aging and cycling? |
| Viscosity and cure | Flow and processing window of uncured LSR | Shear rate, temperature, mix ratio and laboratory cure condition | Can the selected material fill, vent, cure and demold in this tool? |
| Density and shrinkage | Early mass, costing and tool-compensation estimates | Temperature, cure, pigment and specimen or part geometry | What do mold trials show for this grade and this part? |
Hardness is a control value not a complete performance model
ASTM D2240 defines durometer hardness as an empirical indentation test. The result depends on the indentor geometry, applied force and the material’s viscoelastic response, and the standard cautions that there is no simple relationship between different durometer types. In practical terms, a Shore A value is useful for material control and sample comparison, but it does not predict every aspect of bending, sealing force or hand feel in a finished component. [3]
Wall thickness and geometry often influence perceived stiffness as much as a modest hardness change. We therefore prefer to compare physical samples in the intended geometry when feel, snap, valve movement or assembly force is critical.
Tensile and elongation values require the same test conditions
ASTM D412 covers tensile testing of vulcanized rubber and thermoplastic elastomers. Its public significance statement notes that tensile results depend on extension rate, temperature, humidity, specimen geometry and pretest conditioning, and that materials should be compared under the same conditions. It also states that tensile properties alone may not directly describe total end-use performance. [4]
This matters for custom silicone parts because many failures begin at a molded feature that is absent from a standard dumbbell specimen: a sharp transition, a hole, a slit, a thin lip, an insert edge or a gate vestige. Use the TDS to shortlist grades, then test the actual component under the intended load and assembly sequence.
A laboratory cure condition is not a production cycle promise
Supplier tables often state a cure schedule used to prepare test specimens. That schedule tells you how the published cured properties were generated. It does not necessarily define the time required in an injection mold or compression tool. Dow’s current liquid silicone rubber selection guide explicitly says its listed cure conditions are the parameters used to test rubber properties and do not reflect actual injection-molding cure time. [5]
Production cure depends on material temperature, mold temperature, part thickness, tool layout and process settings. For this reason, we confirm cycle and demolding behavior through the selected material, tool design and mold trial rather than copying a TDS laboratory cure time into the quotation as a guaranteed cycle.
Separate regulatory statements from engineering properties
A TDS may mention food-contact regulations, USP Class VI, selected ISO 10993 tests, REACH status or another documentation framework. Read the wording and the limitations carefully. “Formulated to meet,” “tested according to,” and “compliant with” are not interchangeable statements, and none of them removes the product owner’s responsibility to evaluate the finished article for its exact market and use.
The project team should identify the target country, contact type, duration, temperature, cleaning or sterilization process and any color or additive. Then request the grade-specific documents that apply to the final formulation. If a claim is important to the product label or technical file, the responsible regulatory team should confirm what evidence is sufficient.
Turn the TDS into a finished part approval plan
After the team selects a candidate grade, translate the material information into requirements that can be checked on production-representative parts. We recommend separating three levels of evidence.
| Evidence level | Purpose | Typical project record |
|---|---|---|
| Supplier material data | Screen candidate grades and processing routes | Approved grade and revision; TDS; SDS; grade-specific declarations; color or additive record |
| Part conformance | Confirm that supplied parts match drawing and workmanship requirements | Critical dimensions; hardness method; appearance sample; flash limit; material identification; agreed sampling |
| Application validation | Confirm that the assembled product performs in intended service | Fit, sealing, flow, cycling, aging, chemical or cleaning exposure, and regulatory evaluation as applicable |
This structure avoids two opposite mistakes. The first is asking the molder to guarantee every typical TDS value on every finished part, even when the published method uses a standard laboratory specimen. The second is accepting only a supplier data sheet and never defining how the finished component will be inspected or functionally tested.
A practical review sequence for a new custom silicone part
How DX can support the material discussion
At DX, we help you select silicone materials based on the performance your part needs and the conditions it will face in use. We support custom projects with liquid injection molding, compression molding, extrusion and overmolding, together with tooling, secondary operations and assembly. Our quality control capabilities include incoming-material and production checks for hardness, tensile strength, tear strength, compression set and dimensions. We work with you to define which checks and acceptance criteria are relevant to your specific part. [6, 7]
The exact plan still needs to be defined for each project. A useful request for quotation should include:
If the material is not yet selected, send the performance problem instead of forcing a generic specification. We can discuss whether the project is better suited to LSR injection molding, compression molding, extrusion or an overmolding approach, then align the candidate material, tool and trial plan.
Build the specification around the finished product
A good silicone rubber technical data sheet helps us ask better questions. The approval decision should still be based on the exact grade, a manufacturable design and evidence from representative parts. If you are developing a custom seal, valve, gasket, overmolded component, wearable part or other silicone product, send DX your drawing, dimensions, application conditions, material target and expected quantities. Our team can review the material and manufacturing assumptions with you before tooling and sampling. Contact DX to discuss your custom silicone product.
References and source notes
2. KCC Silicone — Liquid Silicone Rubber product table and test-condition notes
3. ASTM International — ASTM D2240-15(2021), Rubber Property Durometer Hardness
4. ASTM International — ASTM D412-16(2021), Vulcanized Rubber and Thermoplastic Elastomers Tension
5. Dow — SILASTIC Liquid Silicone Rubber Product Selection Guide
6. DX Silicone — Customization
7. DX Silicone — Quality Control
Source note: Sources and DX website pages were checked on November 4, 2026. ASTM standards are summarized from their public scope and significance statements; project specifications should refer to the licensed full text where applicable. Material examples are included to explain how to read supplier documentation and do not claim that DX has qualified or used the cited grades. Recommendations and checklists in this article are DX editorial guidance and should be adapted to each application.
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