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Building them. Most seats have a basic frame, and a spring mesh. Many have solid backs, but they can be cut to remove more weight, or you can make your own seat. The "suspension"part is nylon mesh or fabric, similar to a lawn chair. Lay out the fabric, install grommets in each side, and fasten it to the frame using hog rings, or nylon para-cord. Ugly as sin, but light and comfortable.