The system applies to our childrens nylon and polyester waterproof product. There is a special red seam on the inside lining of the arms and legs which can be unpicked to extend the length of the garment by roughly one size. This allows the garment “to grow” normally at the same rate as the child and in most cases in size over a full season. Remember to use a seam ripper when you loosen the stitching so the fabric will not be damaged.