Fabric vertical blinds can often lose their stiffness with age. Instead of purchasing new blinds, you can save yourself money and re-stiffen your old ones by doing it yourself.
Purchase a stiffening agent from a craft or fabric store. Most fabric stores sell spray starches or spray stiffeners, as well as stiffeners in the bottle. Stiffeners sold by the bottle will yield a much stiffer result without multiple layers of application, as well as a more permanent application. If you cannot find stiffener sold by the bottle, you can purchase a fabric and craft glue, which can be diluted with water. To dilute fabric and craft glue, mix equal parts of glue and water in a mixing bowl with a spoon or spatula.
Pour a small amount of stiffening agent into a mixing bowl or old plastic container. Different stiffeners may yield various results, so you may want to test the stiffener on a small corner of your blinds using the foam brush. Let the stiffener dry before you apply it to the rest of your curtains. Based on the test sample, you may choose to dilute the stiffener by stirring in small amounts of water.
Close your blinds so that each slat is facing into the room. Close your windows as well; a breeze may cause your blinds to stick to one another before they have dried. Pour the remainder of the stiffener into the mixing bowl. Stand on a sturdy chair, stool or ladder while evenly applying the stiffener at the top of the first slat with the foam brush. Work your way down to the bottom of the first slat, and then move on to the next slat. Applying the stiffener by completing one slat at a time will yield a more even application and will help to avoid streaks in the finished product.
When you have completed applying the stiffener to each slat, allow the blinds to dry. Avoid opening the blinds while the stiffening agent is drying. Do not use a fan to aid in the drying process; it will cause the blinds to stick to one another before they have finished drying. Once your blinds are dry, you may apply another coat of stiffener if the desired stiffness has not been reached with the first coat.