A switching chamber for a gas-insulated circuit breaker, comprising: two arcing contacts movable relative to one another along an axis (XX 1 ), a main insulating nozzle and an auxiliary insulating nozzle both extending around the axis (XX 1 ) such as to delimit an arcing region , a thermal volume for storing insulating gas, a thermal channel extending between an outer surface of the auxiliary insulating nozzle and an inner surface of the main insulating nozzle so that the thermal channel connects the thermal volume to the arcing region , wherein the thermal channel comprises a first part opening in the thermal volume , a second part opening in the arcing region , and a bend part connecting the first part to the second part so as to achieve a 90 degrees turn, wherein the bend part is delimited by a portion of the outer surface of the auxiliary insulating nozzle including a first bend section (B1) on a thermal volume side, a third bend section (B3) on an arcing region side, and a second bend section (B2) connecting the first bend section (B1) to the third bend section (B3), characterised in that the bend part is delimited by a portion of the inner surface of the main insulating nozzle including a fourth bend section (B4) on a thermal volume side, a sixth bend section (B6) on an arcing region side, and a fifth bend section (B5) connecting the fourth bend section (B4) to the sixth bend section (B6), wherein in axial section view, the first to sixth bend sections (B1-B6) form 30 degrees arcs of circles having respective radii R1, R2, R3, R4, R5 and R6, wherein R1 > R2 > R3 and R4 > R5 > R6. two arcing contacts movable relative to one another along an axis (XX 1 ), a main insulating nozzle and an auxiliary insulating nozzle both extending around the axis (XX 1 ) such as to delimit an arcing region , a thermal volume for storing insulating gas, a thermal channel extending between an outer surface of the auxiliary insulating nozzle and an inner surface of the main insulating nozzle so that the thermal channel connects the thermal volume to the arcing region , wherein the thermal channel comprises a first part opening in the thermal volume , a second part opening in the arcing region , and a bend part connecting the first part to the second part so as to achieve a 90 degrees turn, wherein the bend part is delimited by a portion of the outer surface of the auxiliary insulating nozzle including a first bend section (B1) on a thermal volume side, a third bend section (B3) on an arcing region side, and a second bend section (B2) connecting the first bend section (B1) to the third bend section (B3), characterised in that the bend part is delimited by a portion of the inner surface of the main insulating nozzle including a fourth bend section (B4) on a thermal volume side, a sixth bend section (B6) on an arcing region side, and a fifth bend section (B5) connecting the fourth bend section (B4) to the sixth bend section (B6), wherein the bend part is delimited by a portion of the outer surface of the auxiliary insulating nozzle including a first bend section (B1) on a thermal volume side, a third bend section (B3) on an arcing region side, and a second bend section (B2) connecting the first bend section (B1) to the third bend section (B3), characterised in that the bend part is delimited by a portion of the inner surface of the main insulating nozzle including a fourth bend section (B4) on a thermal volume side, a sixth bend section (B6) on an arcing region side, and a fifth bend section (B5) connecting the fourth bend section (B4) to the sixth bend section (B6), wherein in axial section view, the first to sixth bend sections (B1-B6) form 30 degrees arcs of circles having respective radii R1, R2, R3, R4, R5 and R6, wherein R1 > R2 > R3 and R4 > R5 > R6. <EOS>