Parafilm M ® is a semi-transparent, flexible thermoplastic, and in its final form is a highly water proof and water resistant sheet material. It is practically colorless, odorless, tasteless and approximately 0.005" (e.g. 5 mils/ 127 µm) in thickness. The density of the film is reported to be 0.992 g/cc.
The unique properties of Parafilm M® make it ideal and adaptable for many important laboratory uses and techniques. It molds and seals itself tightly around test tubes, flasks, and various instruments and objects with irregular surfaces. The actual composition of Parafilm M is not actually released by the manufacturer, now ever it is described as being a "blend of olefin-type materials". From our own experience using the product quite extensively in our own laboratory environment, we have generally perceived it to be close in description to that of a very low molecular weight polyethyelene with perhaps some additional wax like materials. That is our own interpretation of its composition and not that of the manufacturer. In any case, the maximum use temperature seems to be on the order of 54° C/130° F which happens to be very consistent with the composition of the material to which is described by the manufacturer and also our own independent perception of its composition. We know that the film becomes soft and sticky at about 130 - 150°F (55-66°C).
In electron microscopy and histology laboratory environments, it is useful for wrapping around, as a final kind of seal, any flask or container containing glutaraldehyde, aqueous osmium solution, just to name a few of its many applications in that kind of environment. Remember, for osmium and glut, it was not meant to be the only seal, it is mean to be a back up seal, just one more precaution to take in the event the primary seal (e.g. the ground glass cap) should somehow become dislodged and open up and/or fail.
It is highly insensitive to moisture vapor, moisture loss, and moisture absorption and yet permeable to gasses sufficiently to make it ideal for working with culture media. This property has also made it adaptable and ideal as an "overwrap" for wet bandage and covers in the drainage cases.
The specific gravity of Parafilm M® is 0.922. There is a test done on coal for determining its BTU value and Parafilm M® is used in the protocol and in order to make the correct calculations, the specific gravity of the material is needed.
