Structure‐Driven Thermal Insulation Through Single‐ and Double‐Shell Hollow Silica Nanospheres Via a Single‐Step Sacrificial‐Interlayer Strategy

Achieving ultralow thermal conductivity through systematic control of hollow architectures with thermally and chemically resilient frameworks represents a crucial step toward high‐performance insulation materials. Here, we establish a simplified synthesis strategy enabling direct comparison between single‐shell and double‐shell hollow silica nanospheres, elucidating the structural origins of heat‐transfer suppression in hierarchical silica systems. Polypyrrole serves as a sacrificial interlayer, enabling tunable inter‐shell spacing, precise control of void size, and adjustable shell thickness via single calcination, elucidating direct correlations between structure and thermal transport. Structural analyses reveal single‐shell hollow silica and double‐shell hollow silica nanospheres possess thermally stable, amorphous, hierarchically mesoporous SiO 2 architectures with well‐defined interfaces and abundant phonon‐scattering sites. Systematic comparison confirms that the additional shell and inter‐shell void in double‐shell hollow silica enhance phonon scattering and suppress thermal transport, resulting in an average thermal conductivity reduction of ~28% relative to single‐shell hollow silica. The lowest thermal conductivity achieved was 0.027 W m −1 K −1 under ambient conditions. Increasing inter‐shell spacing further amplifies this effect, demonstrating that rational structural design can outweigh material quantity, achieving lower conductivity even with higher SiO 2 fraction. When embedded in a polydimethylsiloxane matrix, double‐shell hollow silica nanospheres outperform pristine polydimethylsiloxane and single‐shell hollow silica composites, underscoring effectiveness for lightweight, durable thermal insulation. The revealed structure–property relationships provide general design principles for developing nanoscale architectures with ultralow thermal conductivity.