What specific substance was used by the brothers to join the sheets of paper together in the construction of the envelope?

Answer

Paste

A critical, often overlooked dimension of their engineering focused on minimizing the weight of the non-lifting components that formed the structure itself. To successfully join the numerous sheets of paper required to create the necessary large volume, the brothers employed paste. The consistency, application, and quantity of this paste were crucial variables; too much added unnecessary weight, decreasing the potential lift capacity, while too little risked structural failure when the envelope was inflated with hot air. Mastering the reduction of weight in these adhesive elements was as vital as mastering the creation of lift.

What specific substance was used by the brothers to join the sheets of paper together in the construction of the envelope?
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