Reusable vs. Disposable Cups
This classic life-cycle energy analysis was performed
by University of Victoria professor of chemistry Martin
B. Hocking. Hocking compared three types of
reusable drinking cups (ceramic, glass and reusable
plastic) to two types of disposable cups (paper and
The energy of manufacture of reusable cups is vastly
larger than the energy of manufacture of disposable
cups (Table 1). In order for a reusable cup to be an
improvement over a disposable one on an energy
basis, you have to use it multiple times, in order to
"cash in" on the energy investment you made in the
cup. If a cup lasts only ten uses, then each use gets
"charged' for one-tenth of the manufacturing energy. If it
lasts for a hundred uses, then each use gets charged
for only one-hundredth of the manufacturing energy.
But in order to reuse a cup, it has to be washed. The
efficiency of the dishwasher, and the efficiency of the
energy system that powers it, determine how much
energy is required for each wash.1 Hocking assumed
a new, commercial dishwasher running on Canadian
electricity, requiring about 0.18 MJ/cup-wash.2 The
total amount of energy per use is this wash energy
plus the appropriate fraction of manufacturing energy,
depending on the cup's lifetime. Figure 1 shows how
the energies per use of the three reusable cups
decline, the more you use them.
The lifetime needed for the energy per use of a
reusable cup to become less than for a disposable
cup, is called the 'break-even point." In Table 2, the
break-even matrix shows how many uses are
required for each reusable cup to do better than
either disposable cup.
The results are extremely sensitive to the amount of
energy the dishwasher requires for cleaning each cup.
Hocking's choice for the dishwasher, requiring 0.18
MJ/cup-wash, is barely less than the manufacturing
energy of the foam cup, 0.19 MJ/cup. If Hocking had
chosen even a slightly less energy-efficient
dishwasher as his standard, then the reusable cups
would never have broken even with the foam cup.
The lesson of this life-cycle energy analysis is that
the choice between reusable and disposable cups
doesn't matter much in its overall environmental
impact. One should use one's best judgement.
Indeed, in situations where cups are likely to be lost
or broken and thus have a short average lifetime,
disposable cups are the preferred option.
Table 1 - The embodied energy in each of the five cups (last
column) is the cup mass (first column) multiplied by the
material specific energy (second column).
Figure 1 - The energy per use of each reusable cup (black
lines) declines as it is used more times. The energy per use
of each disposable cup (green lines) is a constant equal to
the manufacturing energy, since it is used only once and is
never washed. The numbers in the labels are the
manufacturing energies for the different cups.
Table 2 - Break-even matrix. Each number shows the uses
necessary before the reusable cup listed on the left,
becomes equally energy efficient to the disposable cup
listed on the top.
Source: Hocking, Martin B. "Reusable and
Disposable Cups: An Energy-Based Evaluation."
Environmental Management 18(6) pp. 889-899.
1 Dishwashers generally require less energy than hand washing,
because they make particularly efficient use of the hot water, which
is the most energy-intensive part of washing dishes. U.S
Department of Energy, Energy-Efficient Water Heating,
2 ILEA reports most energy values in megajoules (MJ). A
megajoule is enough energy to bring about 3 quarts of
room-temperature water to boiling.
This summary first printed in the ILEA Leaf, Winter 2002
Last Modified on April 10, 2002.