CustomPartNet
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August 26, 2026
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Updated August 26, 2026
Choosing the right injection molding partner starts with understanding how your material and part geometry affect production. Cooling time alone can account for the majority of a molding cycle, which means it has an outsized effect on part cost and lead time. Comparing suppliers on more than price alone, factors like their process control, cooling channel design, and experience with your specific material can save significant time and money over the life of a program. Browse our supplier network on the right to compare qualified molders, review sample parts, and request quotes.
Of the four stages in a molding cycle (fill, pack/hold, cooling, and ejection), cooling is almost always the longest. The part cannot be ejected until the plastic has solidified enough to hold its shape, and rushing this stage risks warpage, sink marks, and dimensional problems that show up only after the tool is already cut. Because cooling time scales with the square of wall thickness, even small changes in part design can have an outsized effect on cycle time and, by extension, per-part cost.
Estimating cooling time accurately before quoting a job (or before finalizing a part design) helps both buyers and suppliers set realistic expectations. That is where CustomPartNet's Cooling Time Calculator and Thermal Diffusivity Calculator come in.
Thermal diffusivity is a material property that describes how quickly heat moves through a substance, and it is one of the key inputs behind any cooling time estimate. A material with high thermal diffusivity carries heat away from the melt quickly, shortening cooling time. A material with low thermal diffusivity holds onto heat longer, which stretches out the cycle.
Inputs:
Thermal conductivity of the material
Density of the material
Specific heat of the material
Output:
Thermal diffusivity, typically expressed in mm²/s or in²/hr
Thermal diffusivity is not usually something a buyer or supplier measures directly. Instead, it is calculated from properties that are commonly listed on a material data sheet: conductivity, density, and specific heat. Once you have those three values, the Thermal Diffusivity Calculator converts them into a single figure that feeds directly into the cooling time equation below.
Once thermal diffusivity is known, it can be combined with the part's wall thickness and a few process temperatures to estimate how long the part needs to stay in the mold before ejection.
Inputs:
Maximum wall thickness of the part
Thermal diffusivity of the material (from the calculator above, or from a material data sheet)
Melt temperature
Mold temperature
Ejection temperature
Output:
Estimated cooling time, typically in seconds
The underlying relationship is that cooling time increases with the square of wall thickness and decreases as thermal diffusivity increases. In practical terms, doubling a part's wall thickness can roughly quadruple its cooling time, which is one reason designers are pushed toward thinner, more uniform walls wherever the application allows it.
Consider a part molded in a general-purpose ABS with a maximum wall thickness of 3 mm, using a melt temperature of 230°C, a mold temperature of 50°C, and an ejection temperature of 90°C.
Look up or calculate the thermal diffusivity of the ABS grade using the Thermal Diffusivity Calculator. A typical value for ABS falls around 0.08 to 0.11 mm²/s.
Enter the wall thickness, thermal diffusivity, and the three process temperatures into the Cooling Time Calculator.
For these inputs, the calculator returns an estimated cooling time in the range of 15 to 20 seconds, depending on the exact diffusivity value used.
This estimate gives a starting point for cycle time before a mold is ever cut, and it can be compared against actual production data once the tool is running to spot discrepancies caused by cooling channel layout or hot spots in the mold.
For a buyer preparing to request quotes, a rough cooling time estimate helps sanity-check the cycle times suppliers propose. If one supplier's quoted cycle time is dramatically shorter than what the calculator suggests, it is worth asking how their cooling channel design achieves that result, or whether the quoted time accounts for the part's full wall thickness.
For a supplier, these two calculators offer a fast way to sanity-check a quote before committing to a cycle time and price. Because cooling time is usually the largest single component of the cycle, an underestimate here can quietly erode margin on a production run. Suppliers can also use the thermal diffusivity output to compare how a substitute resin might change cycle time on jobs where the customer has flexibility on material.
Thermal diffusivity measures how quickly heat travels through a material. It matters because it directly determines how fast a molded part can cool and solidify, which in turn drives cooling time and overall cycle time.
Thermal diffusivity is sometimes listed directly on a material data sheet. When it isn't, it can be calculated from thermal conductivity, density, and specific heat using the Thermal Diffusivity Calculator.
Cooling time scales with the square of the part's wall thickness. This means a modest increase in thickness can lead to a much larger increase in cooling time, which is why designers are encouraged to keep walls as thin and uniform as the application allows.
Not exactly. The calculation provides a theoretical estimate based on material properties and part geometry. Actual cooling time also depends on mold geometry, cooling channel layout, and how efficiently heat is removed from the mold, so a correction factor is often applied to the theoretical result.
A lower mold temperature generally shortens cooling time because it increases the temperature difference driving heat out of the part. However, mold temperature also affects surface finish and internal stress, so it cannot be lowered without limit.
Yes. Both calculators work with any thermoplastic material as long as accurate thermal conductivity, density, and specific heat values are available for that resin.
Use the estimated cooling time as a baseline to evaluate the cycle times suppliers propose. A quote with a cycle time far below the calculated estimate may indicate optimized cooling channel design, or it may be worth a direct question to the supplier about how that number was reached.
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