Polyethylene glycol (PEG)
Polyethylene glycol (PEG) is a potential water-soluble support mechanism that can be used for 3D printing.
For detailed information see this page.
PEG is a flexible, non-toxic water-soluble wax-like polymer.
Via a random MSDS, here: "Melting Point: Melting point increases as molecular weight increases: PEG 400 = 4-8C (39-46F) PEG 600 = 20-25C (68-77F) PEG1500 = 44-48C (111-118F) PEG 4000 = 54-58C (129-136F) PEG 6000 = 56-63C (133-145F)"
PEGs are used in cosmetics, medicine, used in food and food packaging. They can be used as plasticizers, solvents, water-soluble lubricants for rubber molds; wetting or softening agents, antistatics in the production of urethane rubber, components of detergents, etc.
Jesse Brennan pointed out that Lee Valley sells PEG 1000 and PEG 1450 for CAD$6/lb (USD$11.25/kg). PEG 1000 melts at 37C, PEG 1450 melts at 43C. (PEG x means PEG with a molecular weight of x). Lee Valley is an expensive but high-quality Canadian woodworking tool store. They sell the PEG as a "green wood stabilizer".