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Centipoise and centistokes describe different quantities. A viscosity report for lip gloss should identify which quantity was measured before its numerical value is compared with another report.

Dynamic viscosity describes the relationship between shear stress and shear rate. Kinematic viscosity is dynamic viscosity divided by density.

Keep the units with the quantity

The SI unit of dynamic viscosity is the pascal-second. One centipoise, written cP, equals one millipascal-second, or mPa·s.

Kinematic viscosity has units of area divided by time. One centistoke, written cSt, equals one square millimeter per second, or mm²/s.

These units cannot be exchanged by relabeling a value. Kinematic viscosity is not a second, independent definition of thickness or a quantity that exists only when gravity causes flow.

Density connects the values

For the applicable viscosity and density at the same temperature, the relationship is ν = μ/ρ. Using cP and density in g/cm³ gives the corresponding value in cSt.

A numerical example illustrates the units: 500 cP divided by 0.90 g/cm³ is approximately 556 cSt. These are hypothetical inputs, not measurements of a Sambound product or a recommended lip gloss specification.

Packaging sample showroom.

The two numbers are numerically equal only when density is 1.00 g/cm³ in those units. That equality is a condition, not a general conversion rule.

Match temperature and test conditions

Both viscosity and density can change with temperature. A density measured at one temperature should not be combined casually with viscosity measured at another.

Temperature-driven viscosity changes should not be explained as density changes alone. Molecular interactions and the formulation’s structure also affect flow resistance.

Lip gloss may be non-Newtonian. Its apparent dynamic viscosity can depend on shear rate and, for some formulations, the preceding handling and elapsed time.

Dividing an apparent viscosity by density does not make it independent of those conditions. It also does not make a rotational result equivalent to a capillary test performed under different flow conditions.

What the report can support

A useful report identifies the quantity, units, temperature and measurement method. For a non-Newtonian sample, it also records the relevant shear conditions and conditioning history.

For a lip gloss packaging project with SamBound New Material Technology Company Ltd., information at sambound.com can identify the packaging under discussion. The formulation data must come from the actual sample and its test record.

A single viscosity value cannot establish pickup, wiping or leakage performance. Those outcomes involve the formula and the actual package geometry under defined handling conditions.

Use the correctly identified viscosity result to describe the sample and support a controlled comparison. Keep the component and handling assessment separate from a unit conversion.

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SamBound New Material Technology Company Ltd.

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