Ahimsa Parmo Dharm is the central theme of Jain religion. The Every Micro-organisms should be treated equally. Their lifes are as important as ours. So to not kill those little organisim while doing all kriya (deeds) the Pramarjan (cleansing) is must important. while sitting or sleeping on the floor charavla is used for bhumi pramarjan.
The unn material is very soft that every micro organisim do not get hurt by it. that is why charavla is made of unn.
Keep Following non-violence and increase your virtue.