Why a GLB gets larger after optimization

A larger output does not always mean the tool failed. The new settings may favor a different format or precision, and the input may already be compressed. Compare the original and output extensions alongside the command before changing more settings.

Check whether geometry compression was removed

The Conservative preset does not request Meshopt compression. If the input already uses Meshopt, optimizing with compression off can produce a larger file even when the triangle count stays the same. Choose the Smaller file preset if you want Meshopt in the output and your application supports it.

This native gltfpack 1.3 test reprocesses an optimized version of our CC0 sample. The file grows because the output settings differ, not because more triangles were added. It is an example of why repeated optimization is not guaranteed to keep shrinking a file.

Check texture encoding and precision changes

UASTC can be much larger than ETC1S. It is a quality option, not a smallest-file setting. Similarly, disabling geometry quantization or increasing precision can increase the amount of data. Compare those choices against the settings that produced your input.

A tiny model or texture may also gain metadata or container overhead that outweighs the savings. There is no universal minimum saving. If the new format offers no benefit to your application, keeping the original can be the better choice.

Measure the same quantity on both sides

Compare downloaded file bytes with downloaded file bytes. A browser network panel may show the transferred size after HTTP compression, while a file manager shows the stored GLB size. Neither number directly measures texture memory after loading on the GPU.

Change one setting and compare again

Return to the original input. Match its compression choice first, then check texture encoding and precision. Save each command with its result so you can identify the change that increased the file. Do not compensate for an encoding change by immediately removing more geometry.

Compare ETC1S, UASTC and WebP →

Plan a controlled file-size comparison →

Engine reference: gltfpack