ShipStream's Packing Solutions providers use "Infill" to account for the space you may want to leave inside a container to protect the contents, such as air pillows, packing peanuts, crumpled paper, etc.
In this example you can see that the container has 0.25" of space between the product and the insides of the container and 0.5" of space above and below the products.
If you want to account for Infill in your Packing Solutions, start by creating an "Infill" type Packaging Feature. You can create as many Infill variants as you need.
When multiple items on the same order resolve to different Infills they will be sorted by the Infill Priority and the one with the Lowest number will be chosen.
You can set a Default Infill in the System > Configuration > General > Packing Solutions > Infill section.
This will determine the default Infill that will apply to all products. You can set different values at the Merchant scope to have different defaults for different merchants.
The default value may be overridden at the product level as described below or also via a Preprocess Packing Solution Script.
The "Requires Infill" product attribute allows you to override the default with values "None" to disable Infill for that product or any of the available Infills that exist in the current scope.