The blocks were made from polyethylene [1], the history section of the wiki page states that it was reserved for use in RADAR sets during WWII, this would have

The blocks were made from polyethylene [1], the history section of the wiki page states that it was reserved for use in RADAR sets during WWII, this would have been how he got access to it as he was responsible for the design and manufacture of the British RADAR transmitters. I have been told that he was the first person to try putting colouring into LDPE. This may have been after the Page design though, my mother was the eldest child but wasn't born until 1941. I think we contributed some pictures to the UK Materials engineering society, will ask. [1] https://en.wikipedia.org/wiki/Polyethylene https://en.wikipedia.org/wiki/Polyethylene