You don’t actually need sleeping bag for Poon Hill Trek since it is not too cold even in the peak of the winter (Dec-Jan) and the local lodge provides you double pieces of warm blanket. The blanket or quilt you get for overnight sleep will perfectly sufficient to warm up your body at maximum 3200m high above the sea level. However, those who don’t want to avoid using the blankets provided by local lodges during their Poon Hill Trek, they carry their own sleeping bag. So, you can also carry your own sleeping bag if you want to do so but it is not required if you are worrying about the cold and the dropping temperature at nighttime. You can do your Poonhill Trek without sleeping bag.