EXT said something like:
While I find that new PT wood is in various stages of being soaked
with water and will shrink in width according to the amount of
wetness.
I have found that composite materials do expand, particularly in
length, during summer and shrink in winter. I have some 20 foot
lengths and they can grow about a 1/4 inch in length over the winter
measurements, and they will actually "crawl" or move in one direction
over a number of years, requiring some leverage and banging to get
them back in place. We do have extremes in temperatures, winters down
to zero, and summers up to 100 degrees which can cause these problems.

Huh....Hold on.....please verify.... The composite grows when cold and not
when hot?