In our recent blog post giving an introduction to the vacuum forming process we covered each stage of how plastic products are made using vacuum forming. In this post we will be giving an overview of which plastic materials are suitable for vacuum forming and the individual characteristics of each.

What are thermoplastics?

The term “plastic” is used to describe a wide range of materials that essentially fall into two different groups: thermoset and thermoplastic. Thermoplastics are a material which, due to their molecular structure, soften repeatedly when they are heated and then harden once cooled. These characteristics, combined with their “memory” which enables a formed part to revert back to its original state when reheated, are what make thermoplastics so ideal for vacuum forming.

Which thermoplastics are used for vacuum forming?

There are many different types of plastics that are used in vacuum forming and these are some of the more common ones:

  1. Acrylonitrile Butadiene Styrene (ABS)
  2. Acrylic – Perspex (PMMA)
  3. Co-Polyester (PETG)
  4. Polystyrene (HIPS)
  5. Polycarbonate (PC / LEXAN / MAKROLON)
  6. Polypropylene (PP)
  7. Polyethelene (HDPE)

Each of the vacuum forming materials listed above has a set of characteristics which come from their atomic makeup, properties and range of additives. The ideal characteristics for vacuum forming materials are easy to form with a low forming temperature, thermal strength and good flow, high impact strength, and low levels of shrinkage when cooling.

Some of the materials are classed as “Hygroscopic”. These materials need to be pre-dried in an oven before forming, otherwise they absorb moisture. This excess moisture could pit the surface of the sheet and cause moisture blisters: ultimately resulting in a reject part.

Read on to learn more about these 7 different types of thermoplastics used for vacuum forming , their individual properties and the specific applications to which they are most suited.

1. Acrylonitrile Butadiene Styrene (ABS)

Properties An amorphous thermoplastic which is hard and rigid. It has good weather resistance and contains rubber which gives it its improved resistance to impact. It is popular because it comes in a wide range of thicknesses with different finishes and textures.
Hygroscopic Yes
Strength Good strength
Formability It forms well to a high definition
Shrinkage 0.3 – 0.8% shrinkage rate
Finishing It can be roller cut and guillotined. Machines well with band saws, routers and circular saws, and takes all sprays.
Colours Available in black, white, grey and limited colours.
Applications Suited to sanitary parts, vehicle parts, electrical enclosures and luggage.

2. Acrylic – Perspex (PMMA)

Properties An amorphous thermoplastic which can be worked well after forming and has good clarity. With this material only an extruded sheet is suitable; Cast Acrylic doesn’t respond well as the useable plastic zone displayed is very small. It is often replaced with PETG – see item 3.
Hygroscopic Yes
Strength Medium to high strength
Formability It is sensitive to temperature and can be brittle.
Shrinkage 0.3 – 0.8% shrinkage rate
Finishing It takes cellulose and enamel sprays and is good for working by hand. It is prone to shattering.
Colours Available clear and in solid colours.
Applications Suited to roof domes and lights, baths and sanitary ware, signs and light diffusers.

3. Co-Polyester (PETG)

Properties An amorphous thermoplastic which is popular as it is easy to form. It has excellent fabricating performance and is optically good. It can be sterilised, is resilient to a range of alcohols and acid oils, and is also FDA approved for food applications. It isn’t recommended for use with solutions that have high alkaline levels.
Hygroscopic Pre-drying not normally required
Strength Good strength
Formability It has very good formability, forming to a high definition.
Shrinkage 0.3 – 0.7% shrinkage rate
Finishing It can be printed using paints and inks suited to polyester. It can be saw cut, guillotined or routered. Die cutting and punching can be done up to a thickness of 3mm.
Colours Available clear and in limited colours.
Applications Suited to medical applications, displays and point of sale.

4. Polystyrene (HIPS)

Properties One of the most widely used amorphous thermoplastics on the market. It thermoforms with ease and is available with different patterns and textures. It isn’t particularly suitable for outdoor applications due to poor UV resistance.
Hygroscopic No
Strength Medium to good strength
Formability It forms well to a high definition.
Shrinkage 0.3 – 0.5% shrinkage rate
Finishing It machines well with all methods but needs a special etch primer before spraying.
Colours Available clear (although clarity isn’t comparable with PETG, PC or PMMA) and in all colours. Flocked finish is also available.
Applications Suited to low cost and disposable items such as toys, models, displays, and packaging and presentation materials.

5. Polycarbonate (PC / LEXAN / MAKROLON)

Properties An amorphous material which is hard and rigid. It is clear with excellent clarity and has similar properties to acrylic. It also features high impact resistance and a good fire rating as it self-extinguishes.
Hygroscopic Yes
Strength Very good strength
Formability It forms well to a high definition.
Shrinkage 0.6 – 0.8% shrinkage rate
Finishing It has good machine qualities, takes spray and can be ultrasonically welded, tapped and drilled.
Colours Available clear and in translucent and solid colours. Comes in a variety of embossed textures and in opal and diffuser patterns.
Applications Suited to skylights, aircraft trim, guards and visors, riot shields, machine guards, light diffusers and signage.

6. Polypropylene (PP)

Properties A semi-crystalline material which is prone to sheet sag and has difficult forming characteristics. However it is very flexible with minimum moisture absorption which makes it suitable for a wide range of applications.
Hygroscopic No
Strength Very good strength
Formability It is difficult to form and translucent material turns clear when in its plastic state. Good temperature control and sheet level is essential.
Shrinkage 1.5 – 2.2% shrinkage rate
Finishing It does not take any sprays.
Colours Translucent and available in black, white and other colours.
Applications Suited to medical applications, food containers, luggage, toys, chemical tanks and enclosures.

7. Polyethelene (HDPE)

Properties A semi-crystalline thermoplastic and has very similar forming properties to PP. It has high shrinkage rates and good chemical resistance. Sheet level and good heat control is essential for successful forming.
Hygroscopic No
Strength Very good strength
Formability PE is difficult. PE FOAM is good but needs forming at lower temperatures to prevent scorching the surface.
Shrinkage HDPE 2.0 – 3.5% shrinkage rate.
Finishing Doesn’t take any spray but does take printing with specialist inks.
Colours Available in black, white and colours.
Applications Suited to vehicle parts, caravan parts, enclosures and housings.

Want to find out more?

As the UK’s leading vacuum forming specialists we have over 30 years of technical capability and are experts in using vacuum forming to make plastic products that are attractive, cost effective and durable.

This post provides a brief overview of some of the thermoplastic materials commonly used for vacuum forming. If you want to find out more please feel free to get in touch with an expert today on 01482 646464