I am extremely new to blender, I am attempting to model some sandbag physics for a 3d printing project. I want the sandbags to have a nice look to them.
The video below shows the issue I am having.
I want the sandbag to still retain some of its shape but still deform a little bit when it hits the ground. I have also attached the .blend file too. I wish to eventually create something like this:
https://drive.google.com/file/d/1ZmSZTsNzK_ImuBXawsH8giCsZZE77aDZ/view?usp=sharing
To keep shape uncollapsed can be achieved by tweaking some parameters, but it will be always more "softer" in a center and "harder" in corners where springs are closer to each other without additional geometry (see Nathan's answer).
There is also a big game changer - topology. In your specific case if you go to edit mode select all and search for Un-Subdivide like 2, than under Physics Properties > Soft Body > Field Weights > Gravity set back to 1 ... you can see object doesn't collapse.
You can try Cloth simulation instead, that has an Internal Springs feature. Here I scaled bag to something more real-size (1 x 0.5 x 0.3). Un-Subdivided to 3. Physics Properties > Vertex Mass 10 kg, enabled Internal Springs. Add Collision modifier with Thickness Outer 0.001 and Friction 50.
Soft body physics transmits its forces along the edges of the mesh. There is no such thing as volume for a soft body-- no forces that fill it. It's like one of those childhood craft projects where you make shapes by running string through straws.
If you want to create soft body forces that limit the ability of one side of your bags to reach the other side, you can do this by joining opposite sides of the mesh with new edges. These new edges will resist being compressed or stretched, and will resist bending (if you have bending > 0.)
Unfortunately, they will also screw up your normals. Which is one reason that I always use soft body physics on a non-rendering mesh, and then use a mesh deform modifier to transfer those physics to my rendering meshes.
I've created a small demonstration of the difference of the behavior of soft body with these support edges vs without, as well as a demonstration of how a soft body can be used to deform a different mesh via a mesh deform modifier:
