Why is PrusaSlicer filling negative space on my 3D model
I am trying to print a 3Dmodel of my car. But it is a convertible and there is negative space between the doors where the seats are since there is no roof. When I slice the model PrusaSlicer is infilling the portion of the car below the doors. Does anyone know how to make sure it doesn't infill the negative space. I have included screenshots. I am new to the PrusaSlicer program and 3D printing. 
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RE: Why is PrusaSlicer filling negative space on my 3D model
Hiya and welcome.
First of all from your images I can see that the model is broken. PS has attempted to repair it but it still has over 4000 open edges. 3d models to be printable need to be whats known as manifold. Basically water tight, as in if you had water on the inside of the model it should be able to leak out. Look up the term there are far better explanations on line 🙂
For stuff like this we normally ask for a saved PS project file. Use File>save project As in Prusa Slicer to save a 3mf file. The PS 3mf file is a snapshot of your setup. It has the model, and modifiers, copies of the 3 profiles settings etc. It allows anyone loading it to slice it identically to how you have it when you saved the project. We can then look at the slice preview and settings in greater detail and it saves having to play 20 questions.
However given that PS has already tried to repair the model I would also suggest including the original stl so we can see the original. The forum though is picky about allowed file types. Both stl and 3mf files arent allowed. So you have to ZIP them up before attaching. If you don't the forum will silently just not attach them. No warning, they just wont make it to the post. So please double check afterwards if attaching anything as the edit time is also only a few minutes
Even after the repair I can see from the slice that the repair left missing sections and so isnt printable in its 'repaired' state.
I've seen very similar car models in the past with people wanting help printing them. Unfortunately for those others the models were never designed for 3d printing. They were modelled for rendering, so a game asset or similar. As such they would require completely reworking to make them printable. There was no way an auto repair trying to make a model manifold would ever be successful. Not with current technology anyway. Maybe once they start adding AI into the mix 😉 You may be lucky though, without the project/model its impossible to be sure.
On the filling in parts, you don't have fill holes selected as slicing method do you ? (with a project I wouldn't have had to ask that lol)
So please attach a project and the original model.
RE: Why is PrusaSlicer filling negative space on my 3D model
Thank you for the kind reply, I'm glad this is not a toxic community. I'm having a lot of fun with my new Prusa mini and I'm excited to keep learning. I'm attaching the zip of the STL and 3MF. Thank you for your help.
RE: Why is PrusaSlicer filling negative space on my 3D model
Hi Easter,
the Model shown in the Project file, contains errors, 
If you are using window, you can use the 'Fix through the Netfabb' option. to fix the errors. which may resolve your issue
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Why is PrusaSlicer filling negative space on my 3D model
Thank you for attaching the files. It as I feared, that model is completely not designed for 3d printing. Same as the other cars people have posted.
This is what it looks like in 3d-tool
See how large parts of it look transparent, its just really badly non manifold. Its the same in Blender. I did try the netfabb fix, but while it fixed some stuff its no where near printable still. There are parts intersecting, all the thousands of non manifold geometry errors, bits of the model don't even connect to others etc. The list is long.
Basically it would take more work to fix it than to just remodel it.
For something like a car you would want to do that anyway so you can more easily split it up to print. Less stair stepping that way usually.
Sorry, I think this one is a lost cause.
RE: Why is PrusaSlicer filling negative space on my 3D model
If you need a 3D model specifically designed for 3D printing, it might be best to consider creating a new model from scratch or finding a different source for a printable car model. Designing a 3D model optimized for 3D printing allows for better control over the geometry and can ensure that the model is properly divided into printable parts.
If you have any specific requirements or need assistance with creating a 3D model for 3D printing, I'd be happy to help you further.