origin of Manila envelopes

[Mary Ellen]

Why are they called manila envelopes?

[Postdog]

Because they are made from manila paper.

[Buenchico]

Manila envelopes are traditionally made from manila (a hemp product) but the name is now applied to these types of brown envelopes irrespective of the paper content.

Chris

[Quizmonster]

Manil(l)a is, of course, the capital of the Philippines. Accordingly, many products of that region of the world were called by names using 'manilla' as the appropriate adjective...manilla hemp, manilla grass, manilla wood etc. The type of envelope you ask about was - as already stated - made from paper derived from manilla hemp.