Here is an analogy: SIPS are like drugs, they enhance the frame, artificially. Lots of people use them. They are created by a refining process, without this process you would only have trees, oil and misc. other stuff. They are distributed through an agent. They cause side effects, a house that is too tight, off gassing(did they fix that) and a possible waste by product, what do you do with the material at the end of it's life. They are quick to install offering instant results, a high.

Clay, on the other hand, is the yin of sips yang.

Tim