The standard-sized YubiKey (such as the YubiKey 4, YubiKey NEO, and FIDO U2F Security Key, as well as the YubiKey Standard and YubiKey Edge) are made of injection-molded plastic encasing the circuitry, while the exposed elements consist of military-grade hardened gold. Waterproof and crush-resistant, the standard-sized YubiKey attaches to your keychain alongside your house and car keys.
The YubiKey 4C, also designed for keychains, is rugged and has no batteries or moving parts.
The smaller format YubiKey (YubiKey 4 Nano, YubiKey NEO-n,YubiKey Nano, and YubiKey Edge-n), while they can be placed on a lanyard and put on your keychain, are intended to be inserted in a USB port and not removed on a regular basis.
In June of 2016, the YubiKey 4 Nano started manufacturing as a new “molded” form factor. This molded form factor which makes it impossible to insert the Nano in backwards, and provides a waterproof environment for this nano-sized YubiKey. Now the YubiKey 4 Nano devices are now crush-resistant and waterproof.