Shrinkage is the contraction a plastic part undergoes as it cools after moulding. Most of it happens in the tool during cooling, with a little more after ejection as the part settles, so the moulded dimension ends up slightly smaller than the cavity. How much a material shrinks depends on the polymer and the moulding conditions, which is why the values below are typical guides rather than fixed figures. Enter a dimension to estimate the size of each material after shrinkage, and use the table as a quick reference.
Plastic material shrinkage rates calculator
Enter a moulded dimension to see the approximate size of each material after shrinkage. This is a guide only and does not account for differential shrinkage; always confirm against the supplier datasheet.
Material
Shrinkage %
Post-shrinkage dimension
ABS
0.6
99.40
ABS/PC ALLOY
0.7
99.30
ACETAL (POM)
1.8
98.20
ACRYLIC (PMMA)
0.6
99.40
CAB
0.5
99.50
HDPE
3
97.00
LDPE
3
97.00
NYLON 6 (PA6)
1.2
98.80
NYLON 6 (PA6) 30% GF
0.4
99.60
NYLON 6/6 (PA66)
1.5
98.50
NYLON 6/6 (PA66) 33% GF
0.5
99.50
NYLON 11 (PA11)
1
99.00
NYLON 12 (PA12)
1.4
98.60
PEEK
1.1
98.90
POLYCARBONATE (PC)
0.6
99.40
POLYESTER (PBT)
2
98.00
PET (SEMI CRYSTALLINE)
0.4
99.60
PET (AMORPHOUS)
0.4
99.60
POLYPROPYLENE (PP) COPOLYMER
2
98.00
POLYPROPYLENE (PP) HOMOPOLYMER
1.5
98.50
POLYPROPYLENE (PP) 30% TALC FILLED
1
99.00
POLYPROPYLENE (PP) 30% GF
0.5
99.50
POLYSTYRENE (PS)
0.5
99.50
POLYSTYRENE (PS) 30% GF
0.1
99.90
PVC-P (PLASTICISED)
1.5
98.50
PVC-U (UNPLASTICISED)
0.4
99.60
SAN
0.6
99.40
SAN (30% GF)
0.1
99.90
TPE
2.5
97.50
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Compiled from supplier processing datasheets. Last reviewed June 2026. Always follow your material supplier's datasheet for production settings.
Sourcing the material itself? PlastikCity can connect you with material suppliers across the UK and Ireland.
Good to know
Further considerations for plastic shrinkage
A few factors influence how a given material behaves in practice. Many pigments act as nucleating additives, which can increase shrinkage in some polymers.
Fillers and fibres change things further. A filled or fibre-reinforced grade often shrinks differently from the virgin polymer, and where fibres align, a part can shrink less along the fibre direction than across it. That uneven behaviour is known as differential shrinkage.
As a rule, crystalline polymers shrink more than amorphous ones, because their chains pack into an ordered structure as they cool, which takes up less space.
There are several recognised standards for measuring plastic shrinkage. The most widely used are:
ISO 294-4 and ISO 294-3 (thermoplastic shrinkage).
Shrinkage is the amount a moulded part contracts as it cools from melt temperature to room temperature. It is usually given as a percentage of the original dimension, so a 1% shrinkage means a 100 mm feature ends up about 99 mm.
Why do plastic parts shrink after moulding?
As the polymer cools it becomes denser and takes up less space. Most of the shrinkage happens in the tool during cooling, with a little more after ejection as the part settles, and a small amount can continue for hours or days until temperature and moisture stabilise.
Do crystalline or amorphous plastics shrink more?
Semi-crystalline polymers such as polypropylene, nylon and acetal generally shrink more than amorphous ones such as ABS and polycarbonate, because their chains pack into an ordered structure as they cool. Glass fibre reinforcement reduces shrinkage.
How is shrinkage allowed for in the tool?
The cavity is cut larger than the finished part so that, once the moulding has shrunk, it comes out at the right size. The toolmaker applies the material's shrinkage rate to each dimension when cutting the steel.
What affects how much a part shrinks?
Wall thickness, melt and mould temperature, holding pressure and time, cooling rate, part geometry, and any fillers or fibres all play a part. Fibre-reinforced grades can also shrink by different amounts along and across the fibre direction.
Important notice and disclaimer. This reference and calculator should be used as an on the spot guide only. Users should always follow the material suppliers' processing datasheets. The data is provided as is and without any representation or warranty of any kind, including that it is fit for any purpose, of merchantable quality, or that it functions as intended or at all. Your use of this data is entirely at your own risk and PlastikCity accepts no liability of any kind.
