They are hairpieces where hair strands are tied on a beige or dark brown lace. The whole point of a lace closure is to prevent you from putting heat on your natural hair. It gives your hair a break from heat and products so that it won’t break off.
A lace closure is basically hair that is attached to lace so that when you sew it onto your braids or attach it to your u part wig you can protect your natural hair from heat and still be able to have a realistic parting.