Yes, and no. you do not need to strip it to take it in. you will be paid less for it un stripped. but, yes, the insulation must be removed before the copper can be recycled into a new product. remember, copper is very recyclable, and can be used and reused over and over. the most common way for the insulation to be removed is by burning it off, so there is some air pollution associated with it. still, it is good to recycle it instead of throwing it in the landfill.