Boat fenders protect the sides of a boat from damage when tying up to a dock or rafting with another boat. These handy devices are designed to be damaged so the hull remains unscathed. However, fenders obtained through a marine supply store can be expensive. Fortunately, homemade substitutes work just as well for considerably less money.
Fill a standard pillowcase with foam packing peanuts and sew it shut. Sew a grommet into one or two corners of the pillowcase to attach lines. This type of fender has the bonus of floating if it falls into the water; however, it is not ideal for high-chafe situations, like extended dock stays, nor will it provide ample protection from a high-energy impact. A peanut bag fender is great for short dock stays and brief rafting.
A rope fender is a more solid long-term solution than a peanut bag, although it has less "give" at impact; so it may not dissipate a striking force as well as a more collapsible version. Rope fenders are traditional and can protect the hull against scrapes and dents for many years. Simply take a long length of nylon rope and tie it in a series of knots until it forms a compact mass large enough to protect the hull.
In a pinch, an empty 2 litre bottle can make an excellent fender--fill it with water, seal it and secure a rope around the mouth of the bottle. Several of these strung together may not be pretty, but they will be effective in the short run. For added hull protection, put the filled bottle inside a small nylon bag filled with an additional barrier like foam or tightly wadded newspapers.
Take several small nylon ditty bags and insert heavy plastic liners. From a craft store, purchase mixes of ballistics gelatin and mix according to the instructions. Allow the gel to form inside the liners, and secure the liners inside the nylon bags. If needed, clamp the mouth of the bag and secure a line. This type of fender will provide better force dispersion for impacts than a rope fender. Its ability to resist chafe will depend on the quality of the nylon, or whether multiple bags can be used to hold the gel insert.