The 30W21S is a 20mm (20-400) aluminum cap with a white pulp/polyethylene liner, typically used on glass bottles, jars and jugs. White pulp/polyethylene lined metal caps are a great general purpose closure. They are ideal for powders and non-acidic food products and consumer products such as jar candles and honey.
Aluminum closures are lightweight caps that have a neutral color. They are commonly made with no color coating, though custom colors are available for specialty applications. These closures can tolerate various temperatures and are resistant to impact fractures. They are applicable with products in high humidity environments, high salt content products, or water. Aluminum metal closures tend to cost more because of the value of its raw material.
This information has been provided as a general guide. It is the customer's responsibility to select the proper container for product and application compatibility.