I’m not sure if I should use low density polyethylene or nylon for my pneumatic lines?

Brotec nylon and polyethylene are both suitable for use in pneumatic systems. You need to consider the burst pressures that you require and the working conditions of the tubing. Nylon has a burst pressure of 1000psi and polyethylene tubing has a burst pressure of 600psi. However, whilst Nylon operates at between -20degC and 120degC, the polyethylene will perform up to 65degC but with a much reduced burst pressure.