Forms a strong, air-tight seal
Parafilm is a common lab sundry item that has fascinating, useful properties. Much like the silicone food-sealing “lids” the Cool Tools recently featured, it can form a strong, air-tight seal over the top of a container. However, it is more self-tacky than silicone (a common complaint of the former tool). Since it’s impregnated with wax, has a more workable texture than static-y plastic cling-wrap, but is even stretchier. It can also be stuck to itself in a pouch shape to form a sort of baggie for small bits and pieces.
The wax melts with moderate heat, so it can be used as a textile bonding layer, much like an iron-on patch. For this reason, it shouldn’t be used to cover hot containers. Furthermore, it is (unexpectedly) useful in grafting plants! The wax is biologically neutral, so it forms a sort of compressive bandage for plants to grow together.
I found out about Parafilm from Evil Mad Scientist Laboratories, a hobby hardware company. They posted a link to an explanational video in their “weekly linkdump”. I also found a particular Amazon review extremely thorough.01/5/18