In the 1920's a product called "Celotex Insulating Lumber" was offered. Its possible that the board shown in the photos above was from Cellotex or similar. Here is a vintage ad aimed at the house building industry ...
Several references to Celotex Insulating Lumber below:
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books.google.com]
These two links refer to Celotex as being used in refrigeration plants, but refrigerator
cars are not mentioned:
[
books.google.com]
[
books.google.com]
Edited 2 time(s). Last edit at 05/09/2018 07:52AM by Rader Sidetrack.