Heat flow sensor comprising: a thermopile comprising a plurality of thermocouples (15a,15b,15c,15d) connected in series, the thermopile having a first side and an opposite second side substantially parallel to the first side, wherein each of the thermocouples is provided with a first portion (13b,13c,13d) of a first electrically conductive material and a second portion (14a,14b,14c,14d) of a different second electrically conductive material and attached to the first portion; a first electrically and thermally insulating layer arranged on the first side; a second electrically and thermally insulating layer arranged on the second side; a plurality of first thermally conductive pads (22a-22c) spaced apart from the thermopile by the first layer and extending substantially parallel to the first side; a plurality of second thermally conductive pads (32b-32d) spaced apart from the thermopile by the second layer and extending substantially parallel to the second side; a plurality of thermally conductive first pillars (23a-23c), wherein each first pillar extends from one of said thermocouples at least partially into the first layer and is attached to a corresponding one of the first pads (22a-22c) and has a length greater than a thickness of the corresponding first pad; and a plurality of thermally conductive second pillars, wherein each second pillar extends from one of said thermocouples at least partially into the second layer and is attached to a corresponding one of the second pads and has a length greater than a thickness of the corresponding second pad, wherein, when viewed in projection onto a thermocouple of said thermocouples, the first pillar which extends from said thermocouple and the second pillar which extends from said thermocouple are offset and completely spaced apart from each other. a thermopile comprising a plurality of thermocouples (15a,15b,15c,15d) connected in series, the thermopile having a first side and an opposite second side substantially parallel to the first side, wherein each of the thermocouples is provided with a first portion (13b,13c,13d) of a first electrically conductive material and a second portion (14a,14b,14c,14d) of a different second electrically conductive material and attached to the first portion; a first electrically and thermally insulating layer arranged on the first side; a second electrically and thermally insulating layer arranged on the second side; a plurality of first thermally conductive pads (22a-22c) spaced apart from the thermopile by the first layer and extending substantially parallel to the first side; a plurality of second thermally conductive pads (32b-32d) spaced apart from the thermopile by the second layer and extending substantially parallel to the second side; a plurality of thermally conductive first pillars (23a-23c), wherein each first pillar extends from one of said thermocouples at least partially into the first layer and is attached to a corresponding one of the first pads (22a-22c) and has a length greater than a thickness of the corresponding first pad; and a plurality of thermally conductive second pillars, wherein each second pillar extends from one of said thermocouples at least partially into the second layer and is attached to a corresponding one of the second pads and has a length greater than a thickness of the corresponding second pad, wherein, when viewed in projection onto a thermocouple of said thermocouples, the first pillar which extends from said thermocouple and the second pillar which extends from said thermocouple are offset and completely spaced apart from each other.