fumigation The wood must be fumigated with methyl bromide. Pallets treated using this method bear the initials MB near the IPPC logo. From 19 March 2010 the use of methyl bromide as a treatment according to ISPM15 has been banned within all EU member states. This is due to causing potential harm to the Earth's stratospheric ozone layer. Treated wood pallets must be stamped on two opposite sides, indicating either HT for heat treated or MB for methyl bromide treatment. Pallets made of non-wood materials such as steel, aluminum, plastic, or engineered wood products, such as plywood, oriented strand board, or corrugated fiberboard do not need IPPC approval, and are considered to be exempt from ISPM 15 regulations. Construction Materials Wooden pallets The production of pallets accounts for 43% of hardwood and 15% of softwood usage in the U.S. The cheapest pallets are made of softwood and are often considered expendable, to be discarded as trash along with other wrapping elements, at the end of the trip. These pallets are simple stringer pallets, and able to be lifted from two sides. Slightly more complex, hardwood block pallets, plastic pallets and metal pallets can be lifted from all four sides. These costlier pallets usually require a deposit and are returned to the sender or resold as used. Many "four way" pallets are color-coded according to the loads they can bear, and other attributes. Wood pallets can pose serious bio-hazard risks as they are susceptible to bacterial and chemical contamination, such as E. coli problems in food and produce transportation, and even insect infestation, and thus the need for ISPM 15. Wooden pallet construction specifications can depend on the pallet's intended use: general, FDA, storage, chemical, export; the expected load weight; type of wood desired: recycled, hard, soft, kiln dried or combo (new & recycle); and even the type of fasteners desired to hold the pallet together: staples or nails. The price of wooden pallets reached a record high during the COVID-19 pandemic, due to increases in the prices of supplies and labor. Types Although pallets come in all sizes and configurations, all pallets fall into two very broad categories: "stringer" and "block" pallets. Various software packages exist to assist the pallet maker in designing an appropriate pallet for a specific load and evaluating wood options to reduce costs. Stringer pallet Stringer pallets are one of the original models of wooden pallets.