From this
THREAD
1. Compile and load your map.
2. mat_specular 0
This turns off reflections.
3. buildcubemaps
The game will pause for a second, and lots of little pictures will flash up the top of the screen.
4. disconnect
If you are not using HDR, you can step to step 11
5. mat_hdr_level 0
Turn off HDR.
6. map “your_map_name”
Load the map again
7. buildcubemaps
8. disconnect
9. mat_specular 1
10. mat_hdr_level 2
11. map “cp_dustbowl”
We need to load another map, to clear the caches of your map contents, otherwise it will not reload any of the cubemaps.
12. Disconnect again, and load up your map. Enjoy!