noun
fleece lining
Refers to the soft, brushed inner surface of clothing, especially sweatshirts and hoodies. The reading うらげ is also used but is less common.
このパーカーは裏毛が暖かい。
This hoodie has a warm fleece lining.
裏毛素材のスウェットを買った。
I bought a sweatshirt made of fleece-lined material.
起毛 refers to the raised nap or brushing process, while 裏毛 specifically means the fleece lining on the inside of garments.
Compound of 裏 (ura, 'back, inside') and 毛 (ke, 'hair, fur'), literally 'inside fur'. The reading うらげ is a rendaku variant.