You'd reckon wrong. 3D prints with a few exceptions are very stable. Here's a nice summary:

The Standard Filaments
PLA (Polylactic Acid): The most popular entry-level material. It is plant-based, biodegradable, easy to print, and comes in many colors. Best for aesthetic models, prototypes, and low-stress indoor parts.

ABS (Acrylonitrile Butadiene Styrene): A petroleum-based plastic that is tougher and more heat-resistant than PLA. Great for mechanical parts, but prone to warping and requires a closed-frame printer.

PETG (Polyethylene Terephthalate Glycol): Balances the ease-of-use of PLA with the durability and temperature resistance of ABS. Highly chemical-resistant, making it a great middle-ground for functional prints.

Flexible and Engineering Filaments
TPU (Thermoplastic Polyurethane): A rubber-like, flexible filament used to print soft-touch items like phone cases, gaskets, and wearable components.

Nylon (Polyamide): An engineering-grade material offering high strength, impact resistance, and durability for functional mechanical parts. It must be kept very dry, as it absorbs moisture easily.

PC (Polycarbonate): Known for extreme strength and high heat and impact resistance. Ideal for tough environments, though it requires high extrusion temperatures.

Specialty & Composite Filaments

Carbon Fiber: Tiny, chopped carbon fibers mixed with a base material (like PLA or Nylon) to increase stiffness and reduce flex. A hardened steel nozzle is usually required.

Wood/Metal-Filled: Base filaments infused with fine wood or metal dust to give prints realistic finishes and added weight, suitable mainly for decorative parts.

PVA (Polyvinyl Alcohol): Water-soluble filament that is commonly used as a dissolvable support structure for complex prints