Parametric Tool to Generate 3D Printable PneuNet Bending Actuator Molds

parPneuNets (pneumatic networks) are a class of soft actuators originally developed by the Whitesides Research Group at Harvard. The PneuNet actuator technology has been a seminal soft robotics innovation and can be considered one of the basic building blocks for silicone based soft robotic designs.

The Soft Robotics Toolkit includes pages with files and instructions for 3D printing and laser cutting a number of premade mold designs to cast PneuNet bending actuators. This documentation set contains a parametric file that can be used to generate an STL file for 3D printing a mold to cast a PneuNet bending actuator with any desired dimensions. The tool can be used to design molds for custom actuators for a specific usage. Or it can be used as a part of teaching, to have students conduct their own experiments on characterizing PneuNet actuators of different geometries.




The tool has been coded in the software program OpenSCAD that can be downloaded and used for free. OpenSCAD is a CAD program that can generate 3D models from written code. These models can be output in different formats, including as a 3D printable STL file.

The code of the parametric file contains a number of variables that can be altered to yield a different actuator design:


These variables include:

  • The dimensions of the interior channel that connects the chambers of the pneumatic network and ("Air_channel_length", "Air_channel_width", "Air_channel_height")
  • The dimensions and spacing of the ribs that create the chambers in the actuator ("Rib_element_width", "Rib_element_depth", "Rib_element_height", "Rib_element_spacing")
  • The thickness of the silicone walls that surround the chambers ("Robot_endwall_thickness", "Robot_sidewall_thickness", "Robot_topwall_thickness")

The variable "Air_connector_length" sets the length of a piece of the actuator that is solid, where tubing for actuation can be inserted and fixed:



"TwistAngle" is used to rotate each rib a specific angle around its vertical axis. This will create an actuator that curls to the side:


The variable "Air_channel_pos_offset" is used to offset the air channel from the middle position:


Finally, the thickness of the walls of the mold itself can also be adjusted ("Mold_bottom_thickness", "Mold_wall_thickness").


Creating a Mold

Generating an STL File

Download and install OpenSCAD on your computer if you do not have it installed already.

Download and open the parametric file.

Adjust the parameters to achieve the desired actuator morphology. Use "Preview" (under the "Design" menu) when you altering the variables, to verify their effect on the design.

Once you have the correct design, choose "Render" (under the "Design" menu) to generate the 3D model.

Then choose: "File" -> "Export" -> "Export as STL" and save the file.

3D Printing the Mold


The mold can be printed on a consumer grade 3D printer (e.g. Ultimaker 2) in PLA or another material.

Import the STL file in the slicing software (e.g. Cura or Simplify3D). Orient the 3D model so that the bottom of the mold is oriented downwards.

Before printing it can be helpful to also add a brim to prevent the mold from curling up at the corners.

Post-processing the Mold

When the mold is printed on an FDM printer there is a chance that some small mistakes will be present on the print. If these are just a few hairs/strings or blobs/zits, you can remove them with an X-Acto knife.

Actuator Fabrication

To use the 3D printed mold to make an actuator the general method for making a two parts PneuNets actuator is followed:

  1. A top part is cast in the mold
  2. A bottom part is made (for these molds, it can be cut from a piece of silicone coated fabric)
  3. The two parts are glued together with uncured silicone
  4. Tubing is attached

More detailed instructions for performing these steps can be found in the documentation of the lasercut PneuNets molds in the Soft Robotics Toolkit.



  • Parametric OpenSCAD file
3dprint-pneunet-parametric-v2.0.zip1 KB