Why is my file so much bigger after baking textures and adding an HDRI, and can I reduce it? The file I'm working on was 1.7 Mb before baking textures onto most of the objects in it and adding a background HDRI, and now it is 17.2 Mb. That's even though all those images are separate files and none are packed into the blender file. Is there a way to determine what is taking the space, and to trim it down?



The above file contains one object not in the comparison file, but that can't explain much of the size difference. The comparison file otherwise is almost identical, even has a few small bits and pieces that have geometry that was pared away in the above version. There were a couple of subsurf modifiers that were applied, but they were extensively optimized. The total vert count is only about 70,000 higher.
First, you can make sure no textures or external data is accidentally packed into Blender by using the File > External Data > Unpack All Into Files function.

Second, Blender keeps orphaned datablocks around until the next time you save the Blender file. So Save the file, close it. And reopen it, doing it a few times can clear any deleted datablocks from the file.

You can also use the File > Save As > Enable Compression setting to make sure the blend file is compressed to save some space. For files larger than a hundred MB, it will take a bit longer to save and open.