This blower has a metal nozzle with a protective plastic cover. An inlet valve is located at the base of the bulb in order to prevent air from entering through the nozzle.
However, while this approach to dusting a sample is widely popular in some laboratories worldwide, in part because once purchased it is perceived to be "free" (e.g. no need to purchase duster cans any more), we do not recommend its use for critical EM applications. The simple matter is that the air in the average room is literally filled with particulates of varying sizes, from particulates you can actually see with the eye to those that are submicron and respirable. So while one might blow away particulates clinging to a sample with the SPI Rubber Bulb Dust Blower, one runs the real risk if depositing new particles, some times more than what had been removed in the first place! And in many laboratories, especially those setting the highest standards for cleanliness, this kind of "duster" is just not thought to be good enough. So we offer this product only because our customers often times ask for this product, but in no way do we want our offering it as part of our product line to have the appearance of being some kind of tacit recommendation (as is the case in general for our EM products) for use in electron microscopy.