This is an 8" x 3.5" piece of Kapton foil that was made, but obviously not used, for a lunar module. This patch was made to cover over electric ports and other areas that the engineers needed access to, during the building of the lunar modules. When the LM was finished, these patches would cover over the access points to protect them from exposure to the suns heat in space and on the moon. There are 18 layers of Kapton foil on this patch, it's marked with the LDW 280 Grumman stock number and it's dated 1968.
I don't know which LM this was made for, but if you have anyway to find out by the LDW number, please let me know.