In today's world, many common and specialty items can be purchased made of either metal or plastic. Some people have preconceived notions that either plastic or metal is the better material, although neither is “better” across the board. Plastic is better suited for some items, metal for others. With still other items, one might be less expensive than the other although they work equally well. Even in such cases, one can be better for some people because of the way in which they use the item.
In a laboratory setting, the decision about whether metal or plastic is more suitable becomes even more complicated. Different types of plastics are available for different uses. Certain chemicals can't be stored or mixed in a metal container, while others can melt through a container made of the wrong kind of plastic. It's always important to determine the right material for any piece of equipment based on how the item is intended to be used, and provide proper employee training on what the tool can and cannot do based on the material it is made of.
The biggest problem with metal is that it corrodes, and can corrode quite quickly in the presence of certain acids, alkalines, or chemicals used in a lab setting. There are certain metals which might work well with certain chemicals, but even they corrode over time due to humidity. Contrary to popular belief, even stainless steel can eventually begin to rust, which can become a problem in a sanitized lab setting. Plastic won't corrode like metals do, but can break down at the molecular level when exposed to certain chemicals or energy sources. When used properly, however, plastics can last a lifetime and be cleaned back to “same as new” condition.
Durability is a similar yet different issue than corrosion resistance. Metal tends to be a stronger material against most common forces, such as falling on a concrete floor. Certain types of plastics can be stronger in certain conditions, other types will easily break in the same scenario. It has to do with how being hard can mean a different thing than being hard to the point of brittleness, and being soft can allow for better resilience against some forces yet allow an item to be easily damaged under other conditions.
Although such general terms are the standard in some industries for judging whether to choose metal or plastic tools and equipment, a laboratory setting usually has a different set of standards based on the type of lab it is and what the people working there do. The people working in lab settings are expected to know the difference between types of plastics and metals and what they are used for. This concept applies to large industrial machinery and small items such as beakers and flasks, or even hand tools such as calipers and stirrers.
An important aspect of metal versus plastics is electrical conductivity. Different metals are better at conducting electricity, but most do conduct it to some extent. Plastics do not conduct electricity, although not all plastics of certain thicknesses are considered adequate insulation against it. Such properties make plastic universally better in certain applications. The wiring for any machine which uses high voltage is going to be adequately insulated, especially if water is part of the machine's function, but plastic parts may be more suitable if there is a chance of electricity skipping from the wiring contacts to the parts the operator touches.
Expense of Manufacture
Generally speaking, plastic is less expensive than metal. There are exceptions to the rule, particularly when comparing intricate injection molded custom plastics when simple bent formed metal parts would be suitable. Generally speaking, the manufacturer is going to be aware of which is the better option based on pricing and durability and make the best tool for the intended job. The exception is when either plastic or metal sells better due to preconceived notions. Such a concept generally has more to do with home appliances and tools than laboratory equipment, as people with proper training through school or work are likely to understand how and why one material works and is better suited for their use.
Plastics generally take less time to turn into final products once the initial setup is in place. That means custom sizes and accessories can be produced and delivered according to the needs of a lab, and replacement parts are likely to be more available when equipment needs maintenance. The manufacturing equipment for plastics tends to be computerized, it take the time of an engineer to pull up the proper program files and perhaps adjust it for specific needs, then plug that file into the production equipment. Metals, on the other hand, often have to be bent or shaped by hand, or at the least require manual setting of machinery to produce the final piece.