The .STL file labels an object for 3D printing.
Just like other files,.STL has a weight, expressed in Bytes.
So, the weight of.STL files changes based on the number of mesh and vectors that it contains.
Let’s see the following example:
Figure a: original 3D model;
Figure B: the same 3D model, but after a standard Make Solid function.
Figure C: The same 3D model, but after a high resolution Make Solid (for parameters, please see Figure D)

MeshMixer can “read” the 3D model exactly how it was exported from the original program.
If you try to modify it with some brushes, for example, try to change or move some mesh, the result will look like there was a mistake in the model, because of asymmetry and low-quality surface.
Now, look back at Figure A, in the bottom right corner of the screen.
You’ll notice there’s the number of triangles and vertex of the current model.
It has 31778 triangles and 15889 vertices.
It weighs 8.30 MB.

As you can see in Figure B, no this model is made up of smaller triangles. They define better the bowed parts of this object.
From what we just said, it follows that this 3D model weighs more than the previous one.
If we activate a standard Make Solid, the result will be as follows:
Vertices: 87057
Triangles: 174114
In other words and referring to graphic designers, when the 3D model switches from “Vectorial” to “Pixel”, it gains weight.
The same way goes for a vectorial file switching to a solid format; it’ll gain weight.

Figure C is the result of a high-detailed Make Solid. This means it has a lot more triangles than the two pics above.
In fact, there are 977401 vertices and 1754802 triangles.
The more triangles and vertices your file has, the heavier it’ll be.
This last 3D model weighs 133 MB.

First click on Update, then on Accept.
You can clearly see how the previous 3 pictures are different in meshes and resolution.
The thickness of triangles and vertices increases as we raise the parameters.