These are hydration backpacks.
They're for EFFICIENCY.
The Big Bang Theory Season 10, Episode 20
You cannot beat
the thermal EFFICIENCY
of the C3.
Breaking Bad Season 2, Episode 10
Allowed me to correct
for the observational EFFICIENCY.
The Big Bang Theory Season 3, Episode 4
and its quantum EFFICIENCY
is off the charts.
The Big Bang Theory Season 12, Episode 7