Introduction: Inflatable Silicone Octopus

In this project, we will be created a 3D printed mold that will allow us to make an airtight bladder made from silicone. We will be using special software from our research lab to help us quickly design a mold for any custom shape. This tutorial will be focused on the design and production of 3D model files for making the mold.

If you want to skip to the bladder fabrication step, you can download the STLs from here and skip to our Bladder Fabrication Tutorial.


  1. Illustrator or SVG editing software
  2. Siloseam Software (available free online:
  3. Want to skip the design phase? --> Download the files (

Step 1: Preparing Your Initial SVG Shape

The above video goes through the design process. Please reference for additional details.

The below instructions were generated using Illustrator CC 22.0.1, although any SVG editor can be used to create a design for a silicone bladder.

Start file: octopus.svg (Thingiverse Files)

  1. Create and load your SVG artwork on a canvas. Aim for a design that is less than the size of your 3D printer bed size.
    1. We like to make designs less than 80 mm x 80 mm to avoid warping issues.
  2. For this octopus design, I want to capture the 3D ellipsoid of the head, so I am going to remove the eyes.
  3. Next, open up the Layers Panel to remove any unnecessary SVG elements.
  4. Next, draw a line wherever you’d like air to be injected into the bladder (i.e., inlets).
    1. You can have multiple inlets, especially for designs that are used to create motion (e.g., a soft robotics grasper).
  5. To save some time with the tool, annotate the marks in your design with the following layer names.
    1. For any bladder geometry, name it BLADDER.
    2. For any inlet geometry, name it AIRTUBE4 for ¼” (outer diameter) air tubes AIRTUBE8 for ⅛” (outer diameter) air tubes
    3. Change the artboard dimensions to match the size of your artwork.

End file: octopus-bladder.svg (Thingiverse Files)

Step 2: Generating the Bladder SVG Geometries

Input: octopus-bladder.svg (Thingiverse Files)

  1. Navigate to the Siloseam Tool
  2. High level app tutorial
    1. The right side panel shows all possible actions that the tool supports. You can either click on the buttons or hit the specified keys. Generally, holding shift + key applies the action to all elements on the canvas.
  3. Delete the artwork on the Siloseam canvas by typing Clear command (SHIFT+ Backspace).
  4. Drag-and-drop the octopus-bladder.svg file over the canvas.
    1. You should see any geometry you labeled as bladder turn pink and any inlet turn gray.
    2. If not, click on the assign dropdown and pick the relevant geometry. Click on the corresponding SVG element. Hit the Assign command [a] to assign the name to the SVG element.
  5. Spot check your design by looking at the Outlines (key = [1])
  6. Generate the mold
    1. Select the bladder and inlet geometries.
    2. Hit the following keys: 1 (Outline), 2 (Generate), 3 (Stylize)
    3. Toggle between different style views
      1. Key 1: Outline view (we recommend to download the file in this view)
      2. Key 2: Stylized view (a pretty view of the mold)
  7. Download the file.

Output: siloseam_design _octopus.svg (Thingiverse Files)

Step 3: Generating the STL Model

To provide long term support for this work, we decided to use third-party software to generate the final 3D model. We use Fusion 360 to generate the model, although any 3D CAD software that supports SVG import can be used.

Input: siloseam_design _octopus.svg (Thingiverse Files)

  1. Create a new sketch and Insert > SVG
    1. Click on any plane
    2. Select SVG File -> siloseam_design _octopus.svg
      1. Important (Fusion 360 only) -- There is a bug in the import routine. You need to scale your artwork by a factor of 1.33 Scale Plane XY → 1.33
      2. Step Wall. Select the registration site geometry (rectangle at end of inlet) and the step geometry - Extrude by 2.00 mm (the base layer height).
      3. Mold Wall. Select the geometry adjacent to the previously extruded step. Extrude by 4.00 mm (the seal layer height + the base layer height).
      4. Base. Select all geometries excluding the bound box. Extrude by –2.00 mm.
    3. Export as an STL.
    4. If making a PVA separator, select the registration site geometry (rectangle at end of inlet), and the bladder geometry. Extrude (and create a New Component) by 0.40mm.

Output (Thingiverse Files):

  • octopus_mold.stl
  • separator.stl

Step 4: Fabricate the Silicone Bladder

Detailed step-by-step fabrication instructions can be found in a similar instructable we made.

The high level steps are:

  1. 3D print the mold and separator
  2. Pour silicone in the mold until it reaching the step wall.
  3. Cure for 3 minutes at 135 F (57 C)
  4. Add the separator.
  5. Pour remaining silicone to fill the mold.
  6. Cure for 15 minutes at 135 F (57 C).
  7. Demold.
  8. Insert an airtube with a barb connector into the inlet and inflate!

A video of the process is included above.