Black & White poly (6mil) is very tough, reflective (The white side reflects 90% of all light) and can be handled on a daily basis without damage or tearing. It is also a good choice for partitioning off spaces ensuring maximum efficiency of your lighting.
Please note:
A "mil" is not a millimetre, it is another standard of measurement used to describe film thickness in the plastic film and poly bag business. Using a micrometer a mil measures @ .001 inch