in the otherwise flat material. Dielectric bonding can be effective in some circumstances, as is ultrasonic welding. Recycling Though Tyvek superficially resembles paper (for example, it can be written and printed on), it is plastic, and it cannot be recycled with paper. Some Tyvek products are marked with the #2 resin-code for HDPE, and can be collected with plastic bottles as part of some municipal curbside recycling programs. DuPont runs a program in the United States where disposable clothing, coveralls, lab coats, medical packaging and other non-hazardous Tyvek disposable garments can be recycled, as well as providing a mail-in recycling program for envelopes. As plastic bag recycling has become more prevalent in the United States, the American Chemistry Council has recommended that plastic film drop-off recycling locations should be able to accept Tyvek. Properties of Tyvek According to DuPont's website, Tyvek fibers are (compared to for a human hair). The nondirectional fibers (plexifilaments) are first spun and then bonded by heat and pressure, without binders. Tyvek is also: Lightweight Has a Class 1 flammability rating Chemical-resistant Dimensionally stabilized Opaque Has a neutral pH Tear-resistant Uses Construction/engineering Large sheets of Tyvek are frequently used as housewrap, to provide an air barrier between the outer cladding of a structure and the frame, insulation, etc., allowing water vapor to pass yet restricting air infiltration. Tyvek was used to cover and protect the Reaction Control System (RCS) thruster ports from water and debris, while the shuttle stack was exposed on the launchpad during the latter years of the Space Shuttle program. The Tyvek covers were dislodged shortly after ignition and before the shuttle cleared the tower, posing no strike risk as the shuttle was travelling below . Tom Sachs used Tyvek for the outer shell of the spacesuits used in his Space Program series of artworks. Government use Tyvek is used by the United States Postal Service for some of its Priority Mail and Express Mail envelopes. FedEx also uses it for some of its document envelopes. New Zealand used Tyvek for its driver's licences from 1986 to 1999. Banknotes Costa Rica (solely their 20 colones bank note, Z series), the Isle of Man, and Haiti have made banknotes from Tyvek. These banknotes are no longer in circulation and have become collectors' items. Fashion/personal use Race bibs, or race numbers are often produced on Tyvek paper, so they are less likely to rip during