<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script> <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <!------ Include the above in your HEAD tag ----------> Fabrics used as thermal curtains or screens are positioned between the crop and the <a href="https://www.autoventllc.com/greenhouse/vent-motors">greenhouse curtain motors</a> ceiling and walls in cold weather to lessen nocturnal heat loss. To keep warm air in the developing area, the curtain must be fitted securely; otherwise, warm air would ascend into the "attic" and limit its effectiveness. Second, they lessen the amount of heated greenhouse air that is required.