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Understanding Shrinkage and Warpage: When Polymers Don’t Hold Their Shape
How the Right Masterbatches Can Make the Difference
If you work in product development, colour selection or masterbatch ordering, it doesn't necessarily mean that you're also a plastics engineer. That’s why today we’re offering an easy-to-grasp overview of a topic that can be crucial when selecting the right masterbatch.
A plastic component or product may come out of the mould perfectly, yet after a while, it may no longer fit quite as intended, with a surface bowing slightly or an edge pulling in. Processors are familiar with these phenomena, which are known as shrinkage and warpage. These two terms are often mentioned together, but they have different causes and effects.
What is behind shrinkage and warpage?
As polymers cool, they contract — this is a normal physical process. The resulting change in volume is called shrinkage, or shrink behaviour.
There are three phases of shrinkage:
- Demoulding shrinkage occurs immediately after ejection from the mould.
- Processing shrinkage occurs roughly 12–24 hours after conditioning under standard climate conditions.
- Post-shrinkage occurs during longer storage or with additional thermal exposure.
The extent to which this occurs depends strongly on the material.
- Amorphous polymers (e.g. PC, PMMA, ABS, PS, among others) have a uniform, unordered structure and therefore exhibit minimal directional variation during cooling, remaining largely dimensionally stable.
- Semi-crystalline polymers (e.g. PP, PE, some POM and PA6 types, among others) consist of ordered and disordered molecular regions. During cooling, the ordered zones densify to different degrees, which is where the risk of warpage arises. Polyolefins are generally more frequently and severely affected.
If different areas of a part contract by different amounts, internal stresses and density differences develop. These often only become apparent after demoulding or during storage, when the plastic part distorts — this is referred to as warpage.
Shrinkage is often higher in the flow direction of the polymer melt, and warpage is particularly visible in geometrically complex parts.
Colour does not change the shape, but it can play a role
Whether a plastic part remains dimensionally stable depends on various factors, including the material used, any fillers and additives, mould temperature, processing conditions and part and mould/tooling design. Parameters such as cooling time and geometry also matter.
Fillers and pigments can subtly modify the cooling and crystallisation behaviour of semi-crystalline polymers. Depending on their type and concentration, organic* pigments can behave differently to inorganic pigments.
Thanks to our colouristics expertise and close collaboration with you, we can select suitable colourants for masterbatch development. One key point is that outcomes always result from the interaction of material, processing and design.
Accordingly, depending on the polymer, process and application, we assess whether low-warpage or warpage-optimised masterbatch development (often called 'warpage-reduced' or 'warpage-free') is required, or whether standard masterbatch is sufficient. Every application is different, and the optimal solution is always developed through dialogue between the processor and the masterbatch specialist.
When low-warpage or warpage-optimised masterbatches make sense
Lifocolor develops these specialised formulations for applications that require high dimensional accuracy (i.e. dimensional stability), or where warpage is a known or likely risk due to the material or processing.
These specialised formulations require selected pigments and other raw materials that are precisely matched to the polymer and the process. Using a standard masterbatch when warpage is known or probable can exacerbate the effect due to unsuitable pigments.
Low-warpage or warpage-optimised masterbatches are technically more demanding and are usually more expensive. Such a solution should therefore always be aligned with the actual requirements. We recommend avoiding ordering a low-warpage or warpage-optimised masterbatch as a blanket measure.
This is often unnecessary — and may be economically disadvantageous — when there is no warpage risk. Our sales colleagues and colourists are happy to support you with the assessment.
Working together towards optimal dimensional accuracy (dimensional stability)
The interaction of material, processing and colourants is complex, and this is precisely where our strength lies. Our experts consider the entire process chain, from the polymer, pigment and carrier resin to the processing parameters.
In close collaboration with our customers, we develop
- precise, robust and
- efficient solutions that
- reliably deliver the required dimensional stability.
This approach unites colour impact and function, creating durable, economical and reproducible results for your plastic products.
Have an application that requires an advanced masterbatch, or even a low-warpage or warpage-optimised variant?
Get in touch via email at or by phone on +49 (0) 9571 789-0.
Further information about our products and additional product information can be found under downloads.
* carbon-based colouring agents, mostly synthetically produced; they are characterised by brilliant colours, but often have lower heat resistance than inorganic pigments