5/32" OD latex surgical tubing (amber)(5 feet). This thin wall tubing (1/32" wall) can be used to make small diameter bladders that inflate to about 3/4" diameter.

KIT TIP:   When making bladders, allow some extra bladder material that will not be filled with fuel to help reduce  breakage rates. A properly sized and filled bladder made from KT21a tubing will have half an inch of extra, uninflated bladder tubing on either side of the fueled portion. One ounce will usually run a hot .049 with an open venturi about 4-5 minutes.

KIT TIP:  With latex bladders function and longevity is quite temperature sensitive.  During hot weather keep your fuel can out of the sun to prevent the fuel from becoming too warm.  Hot fuel can lead to broken bladders. During cold weather keep your fuel around room temperature. Cold fuel can result in inconsistent pressure and poor runs. Too cold of fuel can be identified by a bladder that appears to have an aneurism after the fuel is emptied. Toss that bladder, build a new one and use warmer fuel. I use a plastic "six pak" cooler (intended for soft drinks, it holds three 1 quart metal cans) to help keep fuel from becoming too hot or too cold when the flying field temperature is tending toward the extremes.