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The generalised chemical structure of polyisocyanurate showing the isocyanurate group. The polyols are abbreviated as R-groups.. Polyisocyanurate (/ ˌ p ɒ l ɪ ˌ aɪ s oʊ s aɪ ˈ æ nj ʊər eɪ t /), also referred to as PIR, polyol, or ISO, is a thermoset plastic [1] typically produced as a foam and used as rigid thermal insulation.
Moisture vapor transmission rate (MVTR), also water vapor transmission rate (WVTR), is a measure of the passage of water vapor through a substance. It is a measure of the permeability for vapor barriers. There are many industries where moisture control is critical.
Physical: Hydrophobic (water fearing) are water proof, yet steam permeable -microporous coatings or laminations have pores that are so small that liquid water cannot go through. However, vapor water molecules are many times smaller than the liquid state and can pass through these “micro pores”.
A variant of the metric perm is used in DIN Standard 53122, where permeance is also expressed in grams per square meter per day, but at a fixed, "standard" vapor-pressure difference of 17.918 mmHg. This unit is thus 17.918 times smaller than a metric perm, corresponding to about 0.084683 of a U.S. perm.
Four isomers of Polyisoprene. In principle, the polymerization of isoprene can result in four different isomers.The relative amount of each isomer in the polymer is dependent on the mechanism of the polymerization reaction.
In physics and engineering, permeation (also called imbuing) is the penetration of a permeate (a fluid such as a liquid, gas, or vapor) through a solid.It is directly related to the concentration gradient of the permeate, a material's intrinsic permeability, and the materials' mass diffusivity. [1]
Open-cell foam is porous, allowing water vapor and liquid water to penetrate the insulation. Closed-cell foam is non-porous, and not moisture-penetrable, thereby effectively forming a semi-permeable vapor barrier. (N.B., vapor barriers are usually required by the Building Codes, regardless of the type of insulation used.
Butyl rubber gloves. Butyl rubber, sometimes just called "butyl", is a synthetic rubber, a copolymer of isobutylene with isoprene.The abbreviation IIR stands for isobutylene isoprene rubber.