Plastic beat wood in a pallet test conducted by the U.S. Postal Service, according to results issued earlier this year. The Postal Service rated both twin-sheet thermoformed pallets and structural foam pallets as superior to pressed wood pallets.
Thermoformed pallets were considered best because of four factors - they are lightweight (about 19-20 pounds); they are durable, standing up through 56 test cycles; their cost is low, about $15-$16; and they can be recycled easily.
Structural foam pallets ranked No. 2.
They weathered 20-40 test cycles and cost about 50 percent more than twin-sheet thermoformed pallets.
The Postal Service ranked molded, pressed wood pallets -the ones most commonly found in postal facilities - as the worst. Their performance is nearly 700 percent below the lowest-performing twin-sheet thermoformed pallet and more than 300 percent below the lowest-performing structural foam pallet.
They are comparatively heavy, at about 42 pounds. But they do have one benefit: At about $7, the pressed wood pallet is the cheapest.
Historically, purchase price has been the determining factor with many government con-tracts. That appears to bechanging at the Postal Service. An executive summary says: ``Following this test, all subsequent pallet purchases will be based on reliable, comparative life cycle cost estimates and pallet performance.''
Plastic pallets are sparking the first major change in postal pallets in about 20 years. The Postal Service began using pallets to transport different classes of mail in 1973, using traditional wood pallets made of deck boards and stringers. The nestable, molded wood pallet was introduced in 1977.
Postal officials purchased their first nestable plastic pallets, some 200,000 units, in 1987 and have been buying them ever since.
Plastics - especially thermoformed high density polyethylene ones - scored high on the environmentally friendly scale during the test.
Damaged twin-sheet HDPE pallets can be ground into pellets and extruded into sheets to make new pallets. Thermoformed pallets also use the least amount of materials and last longer before failure.
HDPE structural foam pallets also can be recycled. However, according to the Postal Service, current technologies limit the ability to recycle ``significant amounts'' of structural foam pallets back into new pallets. They are also heavier and use more plastic than the thermoformed pallets.
The Postal Service conducted its Pallet Life Cycle Test in 1994, and reported the results this past spring.
Researchers selected eight pallet manufacturers to represent the three types of pallets. The two-month test included stacking, loading, transporting and unloading a shipment of phone books; lifting and moving the pallets; and examining whether the pallets could be nested together when empty. Damage, deformation and vibration levels were measured on the pallets.