Insect pins come in two materials: black enameled steel or stainless steel.
Stainless steel pins are better for humid environments; this is a higher quality pin (which also means these are more expensive pins - no surprise!).
Interestingly, stainless steel pins are sometimes called "white pins" to differentiate from black enamel pins. Not actually white. Go figure.
Also available in sizes 10, 15, 20 and 25 minutens.