The rain fly is the protective outer later of a tent that covers the tent body. It shields the permeable tent roof from rain and harsh sunlight. As an integral part of the tent, the rain fly is constructed of water-repellant fabric and must be replaced immediately if missing or broken. Tent users are at risk of harmful exposure to the elements without this protective shield.
Obtain the brand name and style model of your tent. Tents come in many shapes and sizes which make the rain fly specific to the tent it covers. The tent brand and model number may be printed at the front or somewhere inside the tent. Eureka tents print the style model inside the tent body or on a small tag stitched to the rain fly edge.
Call the manufacturer of your tent and inquire about replacement parts. Many tent companies such as Eureka, Sierra Designs and North Face offer tent replacement parts including a rain fly. You can obtain replacement parts via phone or through store dealers.
Make your own tent fly if replacement parts are not available or if the cost of a replacement fly is too much. Making your own rain fly may be quicker if you do not have enough time to wait for a replacement. Use durable and waterproof fabrics such as a tarp and cut it to the pattern of your rain fly. Use grommets for holes and nylon ropes to attach it to the tent body. The tarp will provide sufficient rain protection while also trapping condensation, but it restricts ventilation and may be too heavy for backpacking use.