Sayyed Mohammad Al-Musawi, Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to... Answered 1 year ago

The Najis part of the blanket is the specific part which met Najis item with wetness and not all the blanket. 
If your feet is wet and it touches that Najis part, then it becomes Najis and you need to wash it. Even if your feet is Najis and you walk on the ground, the ground will not be Najis unless your feet or the ground is wet.

Wassalam.