A method of securing an elongate electrical heating element to a carrier of a cushion, the method includes: providing a softening device having a body including a feeding passage, a gas passage, and an open cavity; conveying the electrical heating element through the feeding passage; driving heated air from a heat source through the gas passage and into the open cavity; heating the electrical heating element within the open cavity to a heat softening temperature; conveying the heated electrical heating element to a sewing head of a sewing apparatus; and securing the heated electrical heating element to the carrier with the sewing head to form a bending in the electrical heating element, the bending is configured to be secured on the cushion and is not able to be bent into a straight line or reshaped at room temperature without damaging the outer insulating layer or the electrical heating wire.