Comparison of DIY Softbox Lining Materials by nickwheeleroz on Flickr.

Via Flickr:
One of the questions asked in the comments when I built my first large softbox was “would a matte white finish on the interior give a more efficient output?” I had to admit, it had never crossed my mind to use anything other than aluminium foil as the lining material as I just assumed this would be very efficient. After doing a bit of research on the internet I found a table with the following values listed for the reflective efficiency of various materials and finishes:

Mylar: 90% to 95%
Flat White: 85% to 93%
Semi Gloss White: 75% to 80%
Flat Yellow: 70% to 80%
Aluminium Foil: 70% to 75%
Flat Black: less than 10%

This was quite an eye opener. Not just for how inefficient aluminium foil was but how efficient both matte white and particularly Mylar were.

This naturally required further investigation and to test the various lining materials available to the DIY softbox builder I decided to go all Mythbusters and build a softbox prototype testbed. This let me test a couple of new ideas for building a better flash holder and by making the lining removable, let me easily test the light output efficiency of aluminium foil, matte white and Mylar. For good measure I also tested matte black to give a useful baseline for the overall efficiency of the various linings.

The test results are all in the comments: