Here is the reason given for using Tyvek (taken from their site)
A weather resistant barrier is a building's main protection against the damaging effects of the elements. A funtioning barrier must include four basic properties:
* It must have a high level of AIR RESISTANCE - to help prevent drafts, reduce energy bills and resist the flow of moisture laden air through wall cavities.
* It must have a high level of WATER RESISTANCE - to help protect the wall cavity from water that gets behind the cladding.
* It must have moderate to high VAPOUR PERMEABILITY - to promote drying in wall systems.
* It must be DURABLE - to withstand the rigors of the construction site and continue to perform once construction is completed.
DuPont™ Tyvek® HomeWrap® is a non-woven, nonperforated sheet made by spinning extremely fine continuous high-density polyethylene (HDPE) fibres that are fused together to form a strong uniform web. DuPont™ Tyvek® is a unique brand and the only product manufactured this way. This tough, durable and unique structure is not susceptible to the compromises of a perforated material. The fibrous structure is engineered to create millions of extremely small pores that resist bulk water and air penetration while allowing moisture vapour to pass through. DuPont™ Tyvek® HomeWrap® achieves an excellent balance of weather resistance and vapour permeability.
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