There's been a suggestion on another forum that, in addition to changing the extension, you should also edit the file. Replace the line which reads figure with mtlCollection As I said, I'm still fiddling with this one. It isn't helping that the results are inconsistent - a MAT pose can work sometimes (after restarting Poser, for example) and not at other times (after switching to the FireFly renderer, for example). I have tried the mtlCollection edit, and it worked for me; but I also subsequently got that MAT file to work without editing, so your mileage may vary. :/