Progressive Folk

Progressive Folk is a subgenre of progressive rock. Though progressive folk uses more acoustic music, many songs would feature some electric instruments.
Best examples of progressive folk is from Bob Dylan's Highway 61 Revisited, Donovan's albums in the mid-60's, The Byrds "Eight Miles High", Peter, Paul, and Mary's "Norman Normal" (which would later be a Warner Bros. Cartoon of the same name), Buffalo Springfield, particularly from their second album Buffalo Springfield Again, and Simon and Garfunkle's last two albums Bookends and Bridge Over Troubled Water.
British progressive folk bands would include Jethro Tull, The Incredible String Band, Fairport Convention, and The Strawbs to name a few.