Possible Clues:

• Synthetic rubber open to abuse by Frenchman
• Synthetic rubber used for wet suits
• Synthetic polymer often used to make wet suits
• Regularly envelop parcel with a lot of new polymer
• Synthetic used to insulate wet suits
• Synthetic rubber rope found coiled in river at Northampton
• Oil and heat-resistant synthetic rubber
• Rubber prone to distort? Renew after stripping
• Synthetic rubbery polymer
• Never open out, lacking very stretchy polymer