JR wrote:

BTW, don't waste any money on the shellback materials you see in fly
shops; little strips cut from plastic sandwich bags work just fine.

JR

The shellback material you get from flyshops is nicer to work with than
plastic sandwich bags as it is elastic and can be stretched to give a
more arthropodous or chitinous segmented look. However, you can buy it a
fabric shops for considerably less.

Tim Lysyk