The performance requirements for optical filters and mirrors are highly dependent on the material's ability to reflect, absorb, enhance or modify incoming light. This can be accomplished with bulk optical glass materials or through coatings that are applied to a pristine glass substrate. Coatings usually allow significantly more freedom for customized light management design options which can be developed even further when a flat glass material with outstanding optical, thermal, mechanical and chemical properties is used.
BOROFLOAT® borosilicate glass is such a unique substrate and has hence become the material of choice for robust high-temperature resistant dichroic filters, hot and cold mirrors.
 
BOROFLOAT® - The sum of its properties is what makes it unique for functional coatings
1.Exceptionally high transparency
2.Outstanding thermal resistance
3.Excellent mechanical strength
4.Broad range of sizes and thicknesses
High UV transparency down to 300 nm, greater than 92 % light transmittance in the visible and near IR wavelength range, outstanding clarity, low auto-fluorescence and low solarization are specific characteristics of BOROFLOAT® glass substrates used in many optical fields. BOROFLOAT® glass - ideal for hot and cold mirrors due to its outstanding thermal resistance
Hot and cold mirrors either reflect or transmit infrared light and hence require high thermal resistance.
The high boron content in BOROFLOAT® glass lowers the thermal expansion coefficient to 3.25 10-6
 K-1 resulting in excellent resistance to thermal shock and temperature gradients.
The thermal properties of BOROFLOAT® glass (uncoated substrate) are shown below.
Maximum thermal resistance of coated filters and mirrors varies depending on the filter