An article of apparel comprising: a textile substrate including a first surface and a second surface opposite the first surface; and a thermal regulation membrane disposed on the first substrate surface, the thermal regulation membrane comprising a plurality of system reactive components, the system reactive components being selectively engaged in response to conditions of a wearer wearing the article of apparel; the article of apparel being characterised in that: the thermal regulation membrane is applied in a repeating pattern of a plurality of units, each unit thereby defining treated areas and untreated areas along the first substrate surface, wherein the treated areas comprise a discontinuous array of generally linear elements arranged in a plurality of substructures, each substructure formed of a first triangular section and a second triangular section, the first triangular section is a mirror image of the second triangular section, and vice versa, and the untreated areas comprise element channels that separate the linear elements, such that adjacent elements are oriented generally parallel to each other, one or more radial channels that intersect the substructures, a segment channel that separates the first triangular section from the second triangular section in each substructure, and a central aperture defined at the centre of each unit by the plurality of substructures. a textile substrate including a first surface and a second surface opposite the first surface; and a thermal regulation membrane disposed on the first substrate surface, the thermal regulation membrane comprising a plurality of system reactive components, the system reactive components being selectively engaged in response to conditions of a wearer wearing the article of apparel; the article of apparel being characterised in that: the thermal regulation membrane is applied in a repeating pattern of a plurality of units, each unit thereby defining treated areas and untreated areas along the first substrate surface, wherein the treated areas comprise a discontinuous array of generally linear elements arranged in a plurality of substructures, each substructure formed of a first triangular section and a second triangular section, the first triangular section is a mirror image of the second triangular section, and vice versa, and the untreated areas comprise element channels that separate the linear elements, such that adjacent elements are oriented generally parallel to each other, one or more radial channels that intersect the substructures, a segment channel that separates the first triangular section from the second triangular section in each substructure, and a central aperture defined at the centre of each unit by the plurality of substructures. the thermal regulation membrane is applied in a repeating pattern of a plurality of units, each unit thereby defining treated areas and untreated areas along the first substrate surface, wherein the treated areas comprise a discontinuous array of generally linear elements arranged in a plurality of substructures, each substructure formed of a first triangular section and a second triangular section, the first triangular section is a mirror image of the second triangular section, and vice versa, and the untreated areas comprise element channels that separate the linear elements, such that adjacent elements are oriented generally parallel to each other, one or more radial channels that intersect the substructures, a segment channel that separates the first triangular section from the second triangular section in each substructure, and a central aperture defined at the centre of each unit by the plurality of substructures.