Microtherm® microporous insulation vs. Aspen Pyrogel XT aerogel blanket.
Which is the better high performance insulation?
An overview of characteristics, performance, handling, and benefits.
Microtherm® is the global market leader in microporous insulation applications with more than double the market share of its closest competitor. The Microtherm Group has three principal sites located in Europe, the USA, and Japan. It offers global supply and support through these sites backed by a network of Global Partners.
What is a microporous insulation?
A microporous insulation such as Microtherm® is around 90% air, but the air is contained in minute cells between chains of amorphous silica agglomerates of particles from 5 to 25 nm in size - many thousand times smaller in diameter than a human hair.
ASTM C168 – Standard Terminology Relating to Thermal Insulation – defines a microporous insulation as - "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.".
Microtherm® insulation is low in density with a typical range between 170 and 400 kg/m³ depending on the form of the final product.
What is an aerogel?
Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly drawn off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation.
ASTM C168 defines an Aerogel as - "A homogenous, low density solid phase material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The resulting material has a porous structure with an average pore size below the mean free path of air molecules at standard atmospheric pressure and temperature".
It is normal practice to use the specific names “Aerogel” and “Microporous insulation” in order to clearly differentiate between the two insulation materials. The main Aspen Aerogels product is a hydrophobic aerogel blanket, Pyrogel XT, formed by reinforcing the aerogel with a non-woven glass fibre batting.
The density of Aspen Pyrogel XT is typically slightly lower than for a microporous insulation at around180 kg/m³.
Upper temperature exposure limits
The upper temperature limits that Microtherm quote for continuous exposure are defined as the maximum measured temperature at which the insulation shrinks less than 2 % in length and width, in a furnace under 24 hour full soak conditions according to the recognised standards ASTM C356, ISO 2477 and EN 1094-6. This is an extremely demanding performance requirement. In most applications with single sided heating, Microtherm® may comfortably withstand higher temperatures but this cannot be guaranteed as so many different factors can have an influence.
Microtherm® products can be reliably rated for continuous exposure to 1000 °C (around 1830 °F). However, at these very high temperatures, as with all insulation materials, a small amount of irreversible lateral shrinkage will occur after prolonged exposure at the maximum temperature limit and above. As the temperature increases, the particles of silica begin to sinter and fuse together, changing the nature of the structure and increasing the solid conduction component of heat transfer. With Microtherm® insulation this shrinkage is extremely slight and rarely has any influence on the effective performance.
The particle size of a silica aerogel causes it to sinter at a lower exposure temperature with a corresponding structural collapse and increasing irreversible shrinkage. The upper temperature limit quoted in the published data sheets for Aspen Pyrogel XT is only 650 °C (around 1200 °F) although even after prolonged exposure to temperatures above 600 °C (around 1110 °F) it has a tendency to become stiff and inflexible.
Above 600 °C, the E-glass covering used on some Microtherm® products will begin to deteriorate although the products can still be handled and re-used. Microtherm® itself is totally unaffected by this temperature. Alternative covering materials are always available. In the majority of applications this will be unnecessary, particularly if the product is enclosed.
Aspen Pyrogel XT is a flexible blanket reinforced with a non-woven glass fibre mat. In order to present the most objective comparison we will quote published data for both Microtherm® itself and also for a Microtherm® Quilted Panel. Although our Quilted Panel has Microtherm® as its insulation core, the presence of “through stitching” to compartmentalise the Microtherm® and render the panel extremely flexible in three dimensions, also serves to increase slightly the solid conduction element of heat transfer with a small resulting impact on effective product thermal conductivity.
Quilted Microtherm® is available as panels or as SlimFlex® which is a continuous roll of flexible insulation.
All data used for this comparison come from published data sheets on each respective company web site.
Product performance comparison
- It is apparent from a comparison of TC data published for each product that at all exposure temperatures above zero Microtherm® in the form of Block and Moulded Pipe Section is clearly the best product. At 400 °C mean (around 750 °F) it is almost twice as good as Aspen Pyrogel XT. Microtherm® also has the benefit of the much higher working temperature limit of 1000 °C (around 1830 °F) compared to 650 °C (around 1200 °F) for Aspen products.
- Microtherm® Quilted Panel gives almost exactly the same performance as Aspen Pyrogel XT at 200 °C mean (around 390 °F). At 100 °C mean (around 210 °F) it is slightly worse but as temperatures increase it gives a progressively superior performance. At 400 °C mean (around 750 °F) the Microtherm® product is roughly 25% better. This performance difference will continue to increase as the Microtherm® Quilted Panel approaches its upper exposure limit of 1000 °C (around 1830 °F).
Comparison of benefits in applications
For any installation, the ideal product would be fully pre-shaped and available in a thickness that required the least number of layers so that installation time and labour costs are kept to an absolute minimum.
Microtherm® MPS (moulded pipe section) offers all of this in full.
Bends are just as fast to insulate as straight runs with MPS bend assemblies with far less layers to apply – MPS is 25 mm (1”) thick. Microtherm® Slatted Panel can also be up to 25 mm thick for large diameter pipes and ducts. Microtherm® Quilted Panels can be up to 15 mm (0.6”thick).
For fast insulation of straight pipe runs, Microtherm SlimFlex® comes straight from the roll.
In contrast, Aspen aerogel blanket is only available in roll form and is normally cut to shape and fitted on site. The maximum thickness available is 10 mm (0.4”).
Non - Combustibility
Microtherm® is certified as absolutely non-combustible to a number of international standards.
Microtherm® products tested to the European Single Burning Item (SBI) test, EN 13823 achieved Class A1 which is the highest possible rating.
Aspen Pyrogel XT tested to BS EN 13501-1, Reaction to Fire Performance, achieved Euroclass A2.
Microtherm® insulation products are normally supplied at the lowest density which can be handled satisfactorily, consistent with optimum overall performance. When greater resistance to compression is required, higher densities can be supplied. Depending on the product type, the normal density range is from just below 200 to 400 kg/m³.
Handling and shaping
Aspen Pyrogel XT blanket is easy to shape using scissors or a sharp knife. Because of the friability of all aerogel products, shaping of Aspen Pyrogel XT can be rather dusty and the wearing of goggles, gloves, and an appropriate face mask are strongly advised.
Microtherm® products covered in woven E-glass are clean and easy to handle and virtually dust free.
Shaping of these products is simple and fast requiring nothing more than a sharp Kraft knife and a clean working area.
What does this all mean?
It means quite simply that Microtherm® is the best high temperature insulation available.
Because it has an exceptionally low thermal conductivity across its entire operating range, Microtherm® in the form of Block and Moulded Pipe Section is clearly superior to an Aerogel blanket at all temperatures above freezing.
Microtherm SlimFlex® and Microtherm® Quilted Panel, are clearly superior to an aerogel blanket for exposure temperatures greater than 100 °C (around 210 °F) – the higher the exposure temperature, the greater the performance difference.
At 400 °C mean (around 750 °F) exposure temperature, Microtherm® moulded products are twice as effective as Pyrogel XT. This means that only half the thickness is required for equivalent performance. At this temperature, Microtherm® Quilted Panel is 25% more effective than Pyrogel XT.
Only at temperatures below 200 °C (around 390 °F) does the thermal conductivity of Pyrogel XT begin to drop close to the performance of Microtherm®.
Another clear benefit of using Microtherm® is the upper exposure limit of 1000 °C (around 1830 °F) which exceeds the capability of an aerogel product by almost 400 °C (around 750 °F).
Microtherm® is up to four times more efficient than conventional high temperature insulation materials such as Calcium Silicate and Mineral Wool at temperatures around 1000 °C. In practical terms that means only one quarter of the insulation thickness is needed for equivalent performance.
The main benefit of using Aspen Aerogel blanket is that it is particularly easy to shape but because of its friability it generates much more dust during shaping and handling. The Aspen product data sheet recommends the wearing of goggles, gloves, and a face mask when handling the material. It has a limited temperature capability and needs greater insulation thickness because of poorer thermal conductivity. Aerogel blanket is only available as a roll in 5 mm (0.2”) or 10 mm (0.4”) thickness.
Compared with the Aspen product, the obvious benefits of Microtherm® are –
- Lowest thermal conductivity - generally thinner insulation systems made up of fewer layers.
- Much higher temperature tolerance. Continuous exposure capability to 1000 °C (around 1830 °F)
- Wider choice of product forms including moulded and pre-shaped products, flexible panels, and flexible rolls.
- Wider choice of thickness – moulded pipe sections are 25 mm (1”) thick.. Microtherm® Quilted Panel is available in thicknesses from 3 mm (1/8”) up to 15 mm (0.6”), and Microtherm® Slatted Panel is available from 3 mm (1/8”) thick up to a maximum of 25 mm (1”). This availability allows each system to be optimised in thickness for the performance required in the minimum number of component layers.
- Less time needed for fitting, less storage space after delivery, reduced delivery costs.
- Fully pre-shaped insulation systems available allowing fastest possible fitting times – fewer layers of easily handled shaped components. Bends are just as quick to insulate as straight runs!
- Long term product stability – dimensional stability at maximum rated exposure temperature.
- Excellent compression resistance of Microtherm® products that can often be increased further by an increase in product density.
- Microtherm® products are clean in use and can be shaped easily during installation without creating excessive dust.
Microtherm® - cool answers to hot problems.