Duffy is credited on a number of albums as a session musician. They played a slide guitar solo on "Holding On" off The War on Drugs' Grammy-winning album "A Deeper Understanding,", and in 2019 they played on William Tyler's instrumental album "Goes West." Duffy contributed guitar, slide guitar, and bass on the albums "Fading Lines" (2016) and "European Heartbreak" (2018) by Dutch artist Amber Arcades. Duffy played slide guitar on "Seven Words," a 2016 track from the album "Front Row Seat to Earth" by Weyes Blood. Duffy appeared on Mega Bog's albums "Happy Together" (2017) and "Dolphine" (2019). Duffy was a regular member of indie rock musician Kevin Morby's live band from 2015 to 2018, and played guitar, piano, and bass on his 2017 album "City Music". Duffy collaborated with music Jenn Wasner on Wasner's second album as "Flock of Dimes," Head of Roses.