MFR, MFI, and MI

When talking about plastics such as polyethylene and polypropylene, we often use the terms MFR or MI.  This describes how fast the plastic flows when heated to a certain temperature under a certain weight.  The weights and temperatures vary depending on the testing method applied.  The most common are the ASTM D1238 and ISO 1133.

Most of the information I've seen thus far are treat these acronyms as being synonymous with each other.  I've heard however that MFR should be used with polypropylene while MI should be used when talking about polyethylene.

If you're interested in the more technical side you'll find that the MFR of a material is an indirect measure of a materials molecular weight.  Thinking of spaghetti is often helpful.  A bowl of long noodles will 'pour' a lot slower than a bowl of short noodles.

To learn more about the test itself, both Wikipedia and Intertek have good websites.

Photo by aloalosabine (in Japan)