TIPS WITH TONY: Using Additive Fillers to Improve Durability

There are hundreds of thermoplastic materials available for injection molding, and various grades provide strength, durability, impact resistance and many other beneficial attributes. By adding compounded fillers to the equation, you can further increase the durability of your parts.

A component molded with glass-filled nylon to improve durability.

Glass-Fiber Filler
Glass is the most commonly used additive in plastics. Glass-filled materials provide a higher level of strength and rigidity to a part versus an unfilled base material. You can adjust the level of glass in a material depending on your needs, but be cautious as glass can affect how a part turns out dimensionally and cosmetically. We typically see 13 percent and 33 percent glass-filled materials, but occasionally it pushes upwards to 45 percent.

Other Additives and Fillers
There more additives than just glass fiber, and many of these are easily compounded by material manufacturers for your specific needs (or they may already have a pre-compounded material that meets your needs). Glass bead, mineral, metal, carbon, glass mica, talk and Teflon are just a few that Proto Labs has worked with in the past. These fillers can improve:

Strength Conductivity
Chemical resistance Impact resistance
Hardness Flame retardancy
UV stability Heat resistance
Stiffness Lubricity

Challenges with Fillers
Although adding fillers can improve the material properties of your parts, you should to take into consideration the role the additives play during the molding process. All thermoplastics shrink when molded and it’s during this shrinkage where certain additives can be detrimental to your parts. What I mean is that the base material is trying to cool and shrink, but the strands of filler may not shrink at the same rate — this creates warp. How much warp and the direction of the warp is dependent on how the fibers align with one another and your part geometry.

Another molding concern with additive fillers is the exterior cosmetics. Fillers can often negatively affect the appearance of parts, adding dullness or even showing the fibers within the flow lines of the part. The solid plan of attack is to look at your parts application and then weigh the pros and cons of incorporating fillers into the material mix.

The cosmetic impact fillers have includes surface finish dullness.

For additional insight into fillers (and the material selection process in general), companies like Polyone and RTP Company can provide material expertise and resources to help you identify the right material. Our past Design Tip, A Dash of Ingredients in the Thermoplastic Recipe: Glass Filling, Colorants and Other Additives, is a detailed look at additive fillers and our Materials Matter white paper digs even deeper into thermoplastic selection. Both are great resources.

As usual, you can contact one of our customer service engineers at or 877.479.3680 to provide some guidance during the selection process.

Tips with Tony is a weekly feature focused on improving the manufacturability of your parts.

This entry was posted in Tips with Tony and tagged , , , by Tony Holtz. Bookmark the permalink.

About Tony Holtz

Tony is a technical specialist at Proto Labs with more than 10 years of experience ranging from CNC mill operator to mold designer to customer service engineer. While his formal education is in industrial machinery operations, he has extensive knowledge and experience in both traditional and advanced manufacturing processes and materials. Throughout his tenure at Proto Labs, Tony has worked with countless designers, engineers and product developers to improve the manufacturability of their parts.

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