Examples of Flexible and Rigid Materials

The flexibility is the ability of a material to change its shape by bending without breaking. Flexibility is the ability to be malleable, adapt to changes in shape and mobility. It is a mechanical flexibility.

However, it is important not to confuse the flexible – rigid opposition (flexibility) with the soft – hard opposition (hardness). A soft material it can be molded and shaped in multiple ways and not just by bending (its malleability is complete). A flexible material cannot be molded and only accepts shape changes when bending.

A rigid material it may not be hard. For example, wood is a rigid material but has low hardness, since relatively little force is required to pierce it, compared to, for example, steel.

The examples given of flexible and rigid materials they are always relative. For example, him paperboard is among the rigid materials as opposed to paper, orn material made from the same fibers, which is however much more flexible. But cardboard also has a slight flexibility compared to, for example, iron.

On the other hand, there are materials that can be flexible or rigid depending on their thickness. For example, him polyethylene High-density (HDPE) can be flexible in thin sheets, but it is more rigid in thick layers, and it is the material from which objects such as garbage containers or even large pipes are made. Many of the materials described below can be both flexible and rigid.

Examples of flexible materials

  1. Paper. It is a thin sheet of pasta that is made from ground vegetable fibers. Paper is more flexible if it has a lean refinement, that is, its fibers are less hydrated. Papers with hydrated fibers are stiffer.
  2. LDPE / LDPE (Low Density Polyethylene). It is a type of recyclable thermoplastic that is used in flexible packaging, such as bags, self-adhesive film and gloves. Although it is also used in rigid parts of containers (such as bottle caps), it is mainly used in thin sheets that make it very flexible. It is used for its good chemical resistance. It can also tolerate temperatures of up to 80ºC, or 95ºC for short periods of time. Due to its flexibility, it has high resistance to mechanical impacts.
  3. Aluminum. It is a metal not only flexible but also soft, that is, it is extremely malleable. However, it is important to note that in thick layers it becomes stiff. For this reason, aluminum can be used in flexible packaging (even in so-called “aluminum foil”) but also in large rigid structures of all sizes, from food cans to airplanes.
  4. Silicone. It is an inorganic polymer. Due to its stability at high temperatures, it is widely used to make molds and adhesives in industry. It is also used sterilized in implants, such as breast implants, valve prostheses and heart.

Examples of rigid materials

  1. Paperboard. It is made up of several layers of a flexible material: paper. However, cardboard is rigid due to its thickness and also due to the process the fibers go through: gluing. It can be made from recycled materials, which makes it a cheap material. Due to its rigidity and low cost, it is the material usually chosen to make boxes that allow other more fragile objects to be transported.
  2. PET (polyethylene terephthalate). It is a highly rigid plastic, but also hard and resistant. It is used in beverage, juice and medicine containers due to its resistance to chemical and atmospheric agents (heat, humidity).
  3. Polypropylene (PP). It is one of the materials that can be considered rigid or flexible depending on its thickness. However, it is mainly used on rigid objects. It is an intermediate between high-density polyethylene and low-density polyethylene. It is very resistant to high temperatures and to most acids and alkalis. They are used in the manufacture of CD cases, furniture, trays and cutting boards. It is a material widely used in gastronomy and medicine (from laboratory furniture to prosthetics) since it does not leave any type of residue or toxic contaminant. It is the material of choice for chemical deposits due to its resistance to them. In its flexible forms it is used in bandages, ropes and threads, but also in thin films used in food packaging.
  4. Glass. It is an inorganic material present in nature. It is rigid and of high hardness, that is to say, it offers a lot of resistance to abrasion, cuts, scratches and penetrations. Despite this, glass objects of all shapes can be made because it can be molded at temperatures higher than 1,200 ºC. Once the temperature drops again, it becomes rigid again in the new acquired shape.
  5. Iron. It is a rigid metal, of great hardness and density. It is the carbide most used by man, in addition to being one of the most abundant materials in the earth’s crust. It is used to create steel, another rigid metal, which is the alloy (mixture) of iron and carbon.
  6. Wood. It is the main content of tree trunks and is always rigid. The flexible “trunks” of plants are called stems and do not contain wood. Wood is used to build rigid objects such as ornaments, tableware, houses, or boats. Unlike other rigid materials such as glass or metals, which can melt to take new shapes, wood is cut, carved or sanded, that is to say that in no case does it stop being a rigid material.