Tyvek is the brand name of a building material from Dupont. It is a type of non-woven membrane commonly known as housewrap or vapor membrane. It is water-resistant but moisture permeable, designed to prevent liquid water from getting into wall cavities but allowing water vapor out to prevent condensation. You can find several products with similar applications: breathable membranes like Tyvek, structural panels with membranes built in and various tar felt papers.
Amowrap is a perforated polypropylene membrane coated with a substance called polyolefin. Unlike Tyvek, which is spun bonded, Amowrap is woven. It can be left open to the sun for up to a year, longer than Tyvek's four months, but must not be exposed to sunlight for more than 12 months.
Although it has a similar sounding name to Tyvek, Typar is made by Reemay, Inc. Like Tyvek it is spun-bonded, but the material is polypropylene rather than polyethylene. Typar has a perforated coating. It is a reflective silver color, and the manufacturer states that it may be left exposed indefinitely, rather than needing to be protected from sunlight.
RainDrop is a cross-woven polyolefin housewrap. It features a contoured surface that the manufacturer claims assists with drainage. RainDrop is UV-stable for four months, but should not be exposed to sunlight for longer than this.
R-Wrap is manufactured by Ludlow Coated Products, who also make Barricade, another brand of housewrap. R-Wrap is made from non-woven polyolefin and is not perforated. It has a high permeability rating, meaning that it transmits water vapor very readily.
Materials that are not housewraps, but which do a similar job to Tyvek, include wall and roof sheathing panels, and tar felt paper. An example of wall sheathing would be Zip System's products, structural panels which include a built-in layer of water and air resistant membrane. Tar felt paper is a traditional material that was used before the invention of polymer housewraps, and which is still favored by some builders for its absorbency and breathability.
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