Short Functional Life
When seeking invaluable solutions, the Invaluablist often looks past plastic. While many useful items are made of it, plastic tends to fall short of other materials with respect to durability. Yes, the plastic itself will probably last an eternity, but too many plastic products have shorter functional lives than their metal competitors.
Lack of Repairability/Bias to Disposability
Another issue with many plastic solutions is they frequently are designed to be discarded, not maintained or repaired. Whereas metals in particular can often be welded or replaced with the removal of a few fasteners, molded plastic components often cannot be so easily repaired. Very often, multiple parts are molded together into plastic, un-fixable agglomerations. Rejecting and avoiding things-disposable—especially plastic things-disposable—is an invaluable hobby.
Susceptibility to Embellishment
The Invaluablist's search for the un-embellished excludes many plastic products because of the material's ease for being formed into stylized designs. Plastic is where you will find all sorts of products molded into cartoon characters and the like. Plastic is also the realm of simulated wood grain. (Need I say more.) Related, where one finds plastic replacing or being appended to otherwise invaluable designs, one finds enhancetropy. Enhancetropy is the death knell of invaluablism for many products.
Sometimes Plastic Excels
In some cases, plastic is the material of choice for fundamental reasons. A saltwater tacklebox, for example, comes immediately to mind as something that might well be preferred to be made of plastic. The advantages of plastic medical supplies are obvious too. And drinkware by the pool should certainly be made of plastic. But, generally, why specify plastic when more natural wood, metal, hide, or other non-plastic solutions exist.
When seeking non-plastic solutions, one often finds the most invaluable products are those that were developed decades ago, before plastic came to dominate our habitats. Non-plastic solutions are out there, but they often require effort to find. (Hint: find many here.)