High-temperature Reusable Surface Insulation (HRSI) is refractory ceramic material used as the basis of the heat shielding of the Space Shuttle. HRSI is refined from sand to form 99.8% (high purity) silica amorphous fibre. Raw HRSI must be combined with a silica-based binding agent & aqua before sintering.

Properties of HRSI

• Resilient to thermal shock - HRSI tiles can withstand a transition from an environment (1200 degrees Celsius) to full immersion in cold water without sustaining any structural damage.
• Rapid Heat Dissipation - The above sample could be handled with an ungloved hand seconds after immersion, even while the core of the tile still glowed red hot.
• Acoustic stress resilience - HRSI tiles can withstand acoustic levels of >165 dB without experiencing structural failure.
• Lack of strength/Porous - HRSI tiling is only 10% material, with the remaining 90% representing void (pores in the material). This form is the cause of the material's excellent refractory behaviour but leads to a lack of tensile strength. The material is also porous as a result.

HRSI is used in conjunction with stronger, waterproof materials in the Space Shuttle heatshielding to give a balance of strength & resistance to the high re-entry temperatures experienced in Earth's upper atmosphere.

HRSI is primarily designed to withstand transition from areas of extremely low temperature (the void of space, about -270 degrees Celsius) to the high temperatures of re-entry (caused by friction between the gases of the upper atmosphere & the hull of the Space Shuttle, typically around 1600 degrees Celsius).