I'll do a paper test by folding an 8.5x11 piece of paper in half and sticking half of it into the unit and closing the lid. If I can easily pull it out easily, I will not buy the cooler. If I struggle a little, I will buy the cooler. /Not wasting your time at all as with everything mass produced you'll get couple of faulty ones. Never done a paper test what i've always done was was lift the cooler just by its lid and give it a gentle shake. Good sealing cooler shouldn't open.