What Is Viscosity?
Viscosity is a measure of a fluid's resistance to flow. Two distinct quantities are measured: DYNAMIC viscosity is measured directly with a rotational viscometer and is common in cosmetic and chemical products; KINEMATIC viscosity is calculated from the fluid's flow time through a capillary tube and is used in oil, fuel and lubricant analysis.
Purpose of Viscosity
The purpose is to numerically determine the product's consistency and verify batch-to-batch consistency. In cosmetics, consistency shapes consumer perception and applicability; in lubricants, the viscosity grade directly defines fitness for use.
Which Products Is Viscosity Applied To?
- Creams, lotions and gels
- Shampoos and liquid soaps
- Paints, adhesives and chemical mixtures
- Engine and hydraulic oils
- Fuels and base oils
In Which Sectors Is Viscosity Used?
Standards Related to Viscosity
- TS EN ISO 2555 (rotational viscometer — Brookfield type)
- TS EN ISO 3219 (plastics — rotational viscometer)
- TS EN ISO 3104 (petroleum products — kinematic viscosity)
- ASTM D445 (kinematic viscosity of transparent and opaque liquids)
- ASTM D2270 (calculation of viscosity index)
- SAE J300 (engine oil viscosity classification)
Viscosity Conditions
- Temperature
- Viscosity is highly sensitive to temperature; measurement temperature is controlled and reported
- Rotational measurement
- Spindle number and rotation speed determine the result; both are reported
- Kinematic measurement
- Typically at 40 °C and 100 °C; the viscosity index is calculated from these two values
- Dwell
- A defined rest period before measurement for thixotropic products
Equipment for Viscosity
- Rotational viscometer and spindle set
- Kinematic viscosity bath and capillary viscometers
- Temperature-controlled water bath
- Stopwatch and automatic flow-time measurement system
- Rheometer (for the flow curve)
Sample Requirements for Viscosity
- Homogeneous specimen free of air bubbles
- Sufficient volume; the container size must suit the measuring geometry
- For thixotropic products, the specimen must be left to rest after mixing
- Measurement temperature and the target viscosity range, if any, must be provided
Duration of Viscosity
The measurement itself is short; duration is set by the specimen reaching equilibrium at the measurement temperature. A measurement made before thermal equilibrium is invalid.
Viscosity Procedure
- 1The specimen is homogenised and air bubbles removed.
- 2It is brought to equilibrium at the measurement temperature.
- 3The appropriate spindle and speed are selected for the rotational measurement.
- 4It is held until the reading stabilises and recorded.
- 5In kinematic measurement, the specimen's flow time through the capillary tube is measured.
- 6The result is calculated in mPa·s or mm²/s.
Viscosity Acceptance Criteria
The acceptance criterion is the viscosity range in the product specification. For lubricants, classification standards such as SAE J300 define limit values for the viscosity grade, and the declared grade must be met.
Evaluation of Results
A rotational value given without stating spindle and speed cannot be compared: for non-Newtonian products, viscosity depends on shear rate and gives a different result at a different speed. Most cosmetic products are non-Newtonian, so the measurement condition is an integral part of the result.
Viscosity Report
- Specimen identification
- Measurement temperature
- Spindle and rotation speed for the rotational measurement
- Measured viscosity value and unit
- 40 °C and 100 °C values and the viscosity index for the kinematic measurement
- Comparison against the specification
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- EU 1223/2009 Cosmetic Products Regulation
- Cosmetics Regulation (Türkiye)
- ISO 22716 (good manufacturing practice in cosmetics)
Kozmetik Testleri — What Does This Testing Field Cover?
The section below describes the field that the Viscosity test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Cosmetics testing shows that a product stays microbiologically safe throughout its use, delivers the performance it claims and contains no restricted substances. There is NO PRODUCT APPROVAL in this family: no authority approves a cosmetic product; responsibility rests entirely with the manufacturer and with the responsible person established in the EU.
This responsibility model shapes how the field works. Before the product is placed on the market a product information file (PIF) is prepared, a safety assessment (CPSR) is carried out and notification is completed. Inspection comes afterwards and asks for the file; if the file is incomplete the product is withdrawn from the market. Test reports form the evidence base of that file.
On the microbiological side there are two different questions and each is answered by a separate test. The CURRENT microbiological quality of the product is measured by enumeration and testing for specified microorganisms. The EFFECTIVENESS of the preservative system is examined by deliberately inoculating the product with microorganisms (challenge test): can the product resist repeated contamination throughout its use? A jar of cream is touched by a finger at every use; the preservative system must cope with that.
On the performance side, claim substantiation studies are carried out. For sunscreens, determination of SPF and UVA protection and measurement of water resistance are mandatory and are the basis of the value declared on the label. Evidence is also produced by in vivo or in vitro methods for claims such as moisturisation, appearance of wrinkles, hair care and colour retention.
On the chemical side, banned and restricted substances are screened: heavy metals, prohibited colorants, preservative concentrations, UV filter levels and contaminants such as nitrosamines. Products containing nanomaterials carry a separate notification obligation.
The BAN ON ANIMAL TESTING is the most defining constraint of the field. Animal testing cannot be carried out on finished products or ingredients, and a product tested on animals cannot be placed on the market. Alternative in vitro methods (reconstructed human skin models, cell culture based tests) are therefore at the centre of the field, and toxicological assessment rests largely on existing data, read-across approaches and in vitro results.
Stability and packaging compatibility studies determine shelf life and the period after opening (PAO). The interaction of the product with its packaging is also assessed: an active substance may migrate into the packaging, and substances that should not be present may pass from the packaging into the product.
On the process side, good manufacturing practice is demonstrated through ISO 22716; this is separate from product testing but a mandatory part of the file.
Method groups in this field
Microbiological quality
Enumeration of aerobic mesophilic bacteria, yeasts and moulds; testing for Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and E. coli.
Preservative efficacy
Resistance of the preservative system to repeated contamination by challenge test (ISO 11930).
Sun protection
In vivo SPF determination, in vitro UVA protection determination, water resistance and critical wavelength measurements.
Chemical analysis
Heavy metals, banned and restricted substances, quantification of preservatives and UV filters, contaminant screening.
Safety assessment
In vitro irritation and sensitisation methods, toxicological risk assessment, exposure calculations.
Stability and compatibility
Real-time and accelerated stability, packaging compatibility, PAO determination, sensory and physicochemical monitoring.
Commonly confused in this field
- There is NO CE marking on cosmetics; conformity is demonstrated through the PIF, the safety assessment and notification.
- The responsible person must be established in the EU; unless the exporter arranges this, the product cannot be placed on the market.
- Microbiological quality and preservative efficacy are different tests; a product that comes out clean may still have a weak preservative system.
- The animal testing ban covers ingredients too; animal test data generated for another market creates a problem of use.
- An SPF claim must be supported by measurement; a formulation change requires a new measurement.
- A change of packaging may require the stability and compatibility studies to be repeated.
Which decisions these results support
- The product information file and the safety assessment
- Verification of the preservative system design
- Substantiation of SPF and efficacy claims
- Determining shelf life and the period after opening
- Compliance with destination market restrictions for export
Related Tests
Frequently Asked Questions About Viscosity
We got different viscosities from different labs — which is correct?
Usually both are correct but the measurement conditions differ. For non-Newtonian products, the result changes with spindle, speed and temperature. All three parameters must match for a valid comparison.
What is the viscosity index?
It is a number showing how much an oil's viscosity changes with temperature, calculated from the 40 °C and 100 °C measurements per ASTM D2270. A higher index means viscosity changes less with temperature.