Campbell Scientific recommends the durable polyethylene jacket and aluminum wrap of the Synflex 1300, ¼ in. outer diameter (OD) tubing (pn 15702).
Standard polyethylene tubing, in contrast, does not have the aluminum layer and, consequently, allows some diffusion through the wall. Standard polyethylene tubing is also harder to work with. The best alternative is to use black polyethylene for UV resistance and to specify a ¼ in. OD with a 0.040 in. wall thickness.