Benefits of Aluminum Blow Molds

Blow molds have unique design freedoms that aren’t possible with injection or compression molds. Many of these benefits are made possible by aluminum. Here’s why aluminum tops steel when it comes to blow molds.


Aluminum molds can be created 10 times faster than steel, so mold delivery is faster and less expensive. What’s more, high-grade aluminum has 50-70% faster cycle times than P-20 steel.

This occurs because aluminum has 5 times higher thermal conductivity than steel, and 8 times higher thermal diffusivity than typical P-20. This rate of heat transfer eliminates the need for costly conformal mold cooling. This also provides greater capacity yields per cavity than other processes.


It’s not only faster to produce aluminum molds, but once they are up and running, they are built to last. Aluminum blow molds are operated under relatively low production pressures, so tool wear is minimal. Millions of parts can be created from a single mold. Aluminum is also easy to weld, insert, modify, and repair.

It’s interesting to note that an aluminum material like QC-10 starts with a Rockwell hardness of 22 but, during use, its hardness increases to 27. That’s right, with more use, aluminum actually becomes more durable. Aluminum surfaces hold up for years of ongoing production.


While some aluminum alloys are stronger than steel, most are a bit weaker. However, what aluminum lacks in brute strength it makes up for in weight: aluminum is much lighter than steel. In fact, steel is about 2.5 times heavier than aluminum, making aluminum the winner in the safety arena during mold building, handling, and set-up.


A handful of blow mold shops are capable of designing and building complex in-mold secondary, decorating, finishing, and assembly operations in aluminum tools. When done correctly, these systems can provide six sigma repeatability and reduce final product costs dramatically.

Because functional performance varies widely between shops, request references. Go with suppliers willing to discuss the long-term performance of their in-mold examples.

Summary comparison of high-grade aluminum vs. P-20 steel

High-grade aluminum vs. P-20 steel
Creation time 10x faster
Cycle times 50%-70% faster
Thermal conductivity 5x higher
Heat transfer 8x higher
Weight 2.5x lighter


You really can’t beat the design freedom, low cost, long life, easy changes, higher output, and faster delivery offered by aluminum blow molds.

If your blow mold tool shop is also part of a full-service blow molding production manufacturer, then you know your tool maker will make sure you have the quality that will last.

Looking for more? Check out our blog on how your blow molder optimizes your product.