The thermal properties of zeolites and related porous solids are essential for their applications. It is currently thought that crystalline porous materials collapse to a dense amorphous state when subjected to temperatures above their thermal stability. [1,2] Herein, an alternative route of amorphization for ordered molecular sieves is revealed that leads to light, template-free, and hierarchical macroporous foams. Simple control of the time and temperature in an ambient atmosphere ensures thermal decomposition and drastic expansion of the microporous titanosilicate ETS-4 (Engelhard titanosilicate 4), [3] which results in progressively low-density (0.73-0.17 g cm À3 ) multichamber bodies with pore sizes that range from less than one to several hundred micrometers. The formation of macroporous foams by thermal disintegration of crystalline microporous solids could be an ideal system for a better understanding of the amorphization phenomenon observed in molecular sieves, and offers a wide range of applications in the context of inorganic porous materials.Porous crystalline materials comprise a large number of solids that are composed of condensed units of various elements. At elevated temperatures, their low-density frameworks compressively collapse to a glass with conventional density.[1] For a number of materials, this process of thermal amorphization is related to the co-existence of at least two amorphous phases with the same composition, but with different densities. [1,2,[4][5][6][7][8] This phenomenon is known as polyamorphism [9,10] and is well-documented for tetrahedral microporous aluminosilicates, namely zeolites. [1,[11][12][13] Polyamorphism in zeolites involves a low-density amorphous phase, which defines the onset of the structural collapse, and a high-density amorphous phase that forms later on further heating. [2] Similar to zeolites, transition-metal silicates show porous-network topologies, but instead of consisting of AlO 4 tetrahedra, the building blocks of the SiO 4 units are combined with MO x polyhedra of various elements. [14] As a prominent member of that family, ETS-4 is a microporous titanosilicate that is known for its anticancer properties [15] and size-adjustable pores for gas separation. [16] The thermal behavior of ETS-4 has been studied profoundly, [16][17][18][19] and although the material has been known since the late 1980s, [3] nothing unusual about its amorphous state is reported. The structure starts to collapse at 200 8C, and it becomes completely amorphous at 500 8C. At higher temperatures (700-800 8C), the amorphous fraction transforms into a dense titanosilicate with narsarsukite structure. [18,20] Herein, we show how the thermal disintegration of ETS-4 reveals a route of amorphization that leads to macroporous structures with progressively expandable pores and low-density frameworks.Macroporous titanosilicate foams were prepared by a onestep method. ETS-4 particles were gradually heated and cooled in air (for details, see the Experimental Section). The structural disinte...