Explore Manufacturing Materials Guides
High-impact polystyrene is one of the least glamorous engineering plastics and one of the most widely used. It is cheap, easy to form and easy to machine, and it fails in specific ways that are worth knowing before a part is designed around it.
What HIPS is made from
HIPS is polystyrene modified with a rubber phase, usually polybutadiene, dispersed through the plastic to absorb impact energy. That modification is the entire point: unmodified polystyrene is hard, clear and brittle, and the rubber phase trades some of that stiffness and clarity for toughness. The result is an opaque, relatively inexpensive material that resists impact far better than general-purpose polystyrene while keeping most of its processing advantages.
| Property | What it means in use |
|---|---|
| Impact resistance | Tolerates knocks that would crack plain polystyrene |
| Stiffness | Lower than unmodified polystyrene but adequate for housings and panels |
| Appearance | Opaque; easy to colour and to texture |
| Machining | Cuts and machines easily with sharp tooling |
| Chemical resistance | Poor against many solvents and hydrocarbons |
| Temperature | Limited; softens well below engineering plastic ranges |
What are the downsides of HIPS plastic?
Chemical, heat and stiffness limits are the main drawbacks.
The three limitations that cause the most trouble are chemical, thermal and structural. HIPS is attacked by many solvents, fuels and hydrocarbon-based cleaners, which makes it unsuitable where it will contact those substances. It softens at temperatures well below engineering plastics, so it cannot be used near heat sources or where it must retain shape under sustained load. And its stiffness is modest, so a thin HIPS part deflects more than the same shape in ABS or polycarbonate.
Two further characteristics are worth planning for. HIPS weathers poorly in prolonged outdoor ultraviolet exposure, developing chalking and colour change unless it is stabilised or painted. And it is prone to stress cracking if it is machined or assembled with locked-in stress, particularly when it then contacts a solvent-based adhesive or cleaner. Both issues are manageable with design and process choices rather than by switching material.
Is HIPS plastic food safe?
Only if the grade is formulated for food contact.
HIPS can be formulated for food-contact applications, but the material alone does not answer the question. Food-contact suitability depends on the specific grade, on the additives and colourants used, and on the intended contact conditions, including temperature and the type of food. A general-purpose HIPS grade is not automatically suitable, and a specification for a food-contact part should name a grade intended for that use rather than rely on the polymer family. Regulatory requirements for food-contact materials are set out by the US Food and Drug Administration.
The practical consequence is that food-contact wording belongs in the specification and on the material certificate, not in an assumption. Where the part is a prototype and the production material has not yet been fixed, saying that the final part will contact food changes which grade is quoted, even if the prototype is made in a general-purpose material for fit testing.
Where HIPS is the right choice
Four applications suit it well. Housings and covers for consumer and industrial products, where impact resistance and cost matter more than stiffness. Point-of-sale and display components, where it is easy to form, colour and print. Prototype parts that will be painted or bonded, since it takes both readily. And vacuum-formed or thermoformed packaging and trays, where its formability keeps tooling costs low.
It is the wrong choice where the part will see solvents, sustained heat, outdoor sunlight without protection, or structural load. Those situations call for ABS, polycarbonate or a higher-performance material, and the price difference is usually smaller than the cost of a failed part. Related thermoplastics and their properties are described under materials.
Machining and finishing HIPS
HIPS machines easily with sharp tooling and moderate feeds, and it produces a clean cut surface without the melting and smearing that softer polyolefins show. The material is relatively soft, so it marks easily, and clamping pressure can leave impressions on a finished face; soft jaws or distributed clamping are worth using on visible parts. Threads are possible but weak, so metal inserts are usually preferable where the joint will be tightened more than once.
Finishing options follow the material’s chemistry. Painting and printing work well with appropriate surface preparation, and solvent-based adhesives need to be chosen carefully because some will attack the plastic. Where a textured surface is wanted, it is usually produced in the mold rather than added afterwards, since machining scratches on HIPS are visible and difficult to blend. Coating terminology and test methods follow ASTM Committee B08, material data is published by ASM International, and drawing conventions follow ASME standards.
Specifying HIPS on a drawing
Name the grade rather than the polymer family, particularly where food contact, impact performance or outdoor use is involved, because additives and rubber content vary. State the surface finish where the part is visible, since the material marks easily. Identify the inserts or threads that carry load, and say whether the part will be painted or printed, because that affects surface preparation and the sequence of operations.
Two ordering details reduce surprises. Where the part will be assembled with solvent-based adhesive, say so, because stress cracking is a real failure mode and it is avoided by design rather than by inspection. And where the part will be used in sunlight, mention it, so an ultraviolet-stabilised grade can be quoted instead of a general-purpose one. Process measurement practice is described by the NIST Manufacturing Extension Partnership, and manufacturing options are set out under CNC machining and injection molding.
Send the part with the environment it will see and any food-contact requirement, and request a quote for machining or molding in HIPS.
FAQ
What is HIPS plastic made from?
Polystyrene modified with a dispersed rubber phase, usually polybutadiene, which absorbs impact energy. The modification trades some stiffness and all of the clarity of plain polystyrene for toughness, producing an opaque and relatively inexpensive material.
What are the downsides of HIPS plastic?
Poor resistance to many solvents and hydrocarbons, a limited temperature range, modest stiffness compared with ABS or polycarbonate, and poor weather resistance outdoors without stabilisation. It is also prone to stress cracking when machined or bonded under locked-in stress.
Is HIPS plastic food safe?
It can be, but only if the grade is formulated for food contact and the additives suit the intended conditions. General-purpose HIPS is not automatically suitable, so the specification should name a food-contact grade and the certificate should confirm it.