Microporous insulation
is a composite material in the form of compacted powder or fibers with an
average interconnecting pore size comparable to or below the mean free path of
air molecules at standard atmospheric pressure. Microporous insulation may
contain opacifiers to reduce the amount of radiant heat transmitted.

The resulting
blend of materials and pore structure produces a thermal insulation with
extremely low thermal conductivity across a broad temperature range. The
Microporous core material is completely inorganic, making it non-combustible
and suitable for passive fire protection applications.

An ASTM
specification for Microporous insulation is under development with the
following Grades and types: Grade 2 Hydrophobic has been chemically treated to
make the insulation water-repellent. The water repellency
is maintained up to its grade operating temperature
of 250°C. Above this temperature it performs as standard Grade 2.

Microporous Board
Insulation

Microporous Rigid
Boards (Type I) are supplied in 2 primary forms. The first, typically identified as block or board, is an
un-faced flat section of Microporous insulation compressed to a density
of typically 18–25 pcf. The second type, identified as panel, is a flat section
of Microporous insulation which has been encapsulated with a high temperature
glass facing to minimize dust and improve handling. Normal densities are 14–18
pcf. Rigid Boards have superior compressive strength but normally cannot be
flexed without cracking or breaking the material. Boards are produced in
thicknesses from ⅛” to 4″ depending on the specific type.

Microporous Flexible
Panel Insulation

Flexible Microporous
Panels (Type II) are manufactured at a lower density of approximately 8–16 pcf.
They are also faced with a high temperature glass facing but also are often
stitched through, in one or two directions, using a high temperature thread.
The lower density and the segregation caused by the stitching allows the
material to be flexed to cylindrical or contoured surfaces. Thicknesses range
from ⅛” to ¾”.

Microporous Pipe
Sections (Type III) are supplied as hollow cylinder shapes split in half
lengthwise or as curved segments. Pipe insulation sections are typically
supplied in lengths of 19.7″ (½ meter), and are available in sizes to
fit most standard pipe sizes. Microporous Pipe Sections are faced with a high
temperature glass facing to improve handling. The thickness is 1″ (25mm).
Thicker insulation can normally be supplied as nested sections for most pipe
sizes. Pipe sections can also be used in combination with Type II Flexible Panels
to meet specific thickness requirements.

With the
exception of Hydrophobic Grade, all Microporous Insulation is permanently
damaged by liquid water. Therefore protective jacketing must be used when the
application is subjected to potential environmental conditions or water spray.
Likewise, care must be taken during transportation, storage, and installation
to prevent contact. Humidity does not degrade Microporous Insulation.

The standard facings for most Microporous
Insulations are high temperature glass fabrics that have a use
temperature that is below the maximum use temperature of the core. In the
majority of applications, the Microporous Insulation is further jacketed,
encapsulated, or sandwiched with other materials in a static environment. In
these environments, the facing provides mainly a handling and installation
benefit. In applications where the product must function dynamically at
temperatures above 800°F, the product should be encapsulated in materials
appropriate for the environment.

Typical values
for thermal conductivity in Btu•in/(hr•ft²•°F) are 0.15 at 392°F, 0.17 at
752°F, and 0.19 at 1112°F. Microporous Insulation has compressive strength of
80 psi for a 10% deflection in a typical board product.

Microporous
Insulation is most often used where a maximum amount of thermal resistance is
needed with minimal thickness and weight. Typical applications include piping
and equipment operating at temperatures above 250°F, tanks, vessels, heat
exchangers, valve and fitting insulation, exhaust ducts, electronic
instruments, and fire protection.