In the development of transparent plastic parts, SAN and MABS are often compared with each other. SAN offers high transparency, good surface hardness, and a low price. However, many manufacturers find it too brittle in actual use: it can crack when dropped, especially in applications involving snap-fits, screw bosses, or contact with disinfectants and cosmetics, leading to recurring after-sales issues. PC has good toughness but is expensive, while PMMA is more brittle and has insufficient heat resistance. MABS occupies the middle ground: it retains transparency close to that of SAN while significantly improving impact resistance and resistance to stress cracking.
So, how should you choose between SAN and MABS? This article presents a clear material-selection framework based on four aspects: transparency and surface hardness, chemical resistance and resistance to stress cracking, compliance for medical and consumer products, and cost and substitution recommendations.
1. Transparency and Surface Hardness
1.1 Light Transmittance and Haze
Both SAN and MABS are amorphous transparent materials with similar light transmittance, although there are some differences.
| Property | SAN | MABS |
| Light transmittance (3 mm) | 89% – 92% | 88% – 91% |
| Haze | Lower; clearer appearance | Slightly higher due to the rubber phase |
| Refractive index | Approx. 1.57 | Approx. 1.54 |
| Pencil hardness | 2H – 3H | HB – 2H |
| Scratch resistance | Good | Average |
| Long-term yellowing tendency | Slow | Slightly faster, especially with butadiene |
SAN has slightly higher light transmittance and lower haze than MABS, giving it a clearer appearance. If your product requires high optical clarity, such as a transparent viewing window, instrument-panel lens, or transparent display cover, SAN is usually more suitable. For ordinary transparent housings, cosmetic packaging, and medical-equipment covers, however, most consumers will find the visual difference between the two materials difficult to notice.
1.2 Surface Hardness and Scratch Resistance
SAN can reach a pencil hardness of 2H-3H, whereas MABS is typically only HB-2H and is relatively softer. This means:
SAN products are less likely to be scratched during routine cleaning, wiping, and use;
MABS products are more prone to fine surface scratches. If a product is frequently touched or cleaned, a hard-coat treatment or protective film should be considered.
However, SAN’s higher hardness also makes it more brittle and more sensitive to notches. Surface hardness and toughness often involve a trade-off, so the choice must be based on the actual loads the product will experience.
Summary: Choose SAN first for transparent parts with high appearance requirements that are not subject to impact; MABS is more suitable for structural transparent parts where the appearance is acceptable but toughness is required.
2. Chemical Resistance and Resistance to Stress Cracking
2.1 Chemical Resistance: Consider the Material, the Medium, and Internal Stress
SAN has good resistance to common chemicals such as acids, alkalis, alcohols, and oils, but it is sensitive to ketones, aromatic hydrocarbons, and chlorinated solvents. Because MABS contains a butadiene rubber phase, its resistance to certain organic solvents, such as ketones and esters, may be slightly lower than that of SAN.
However, the most common practical problem encountered by manufacturers is this: fine cracks appear in transparent parts after contact with alcohol, disinfectants, cosmetics, or cleaning agents. This is often not simply the result of the material dissolving. Instead, the chemical medium penetrates the material surface and reduces local strength, while residual stress from injection molding remains inside the part. Together, these factors cause cracking. This phenomenon is called environmental stress cracking (ESC).
Because of the toughening effect of its rubber phase, cracks propagate much more slowly in MABS than in SAN. In other words, under the same internal stress and chemical exposure, SAN may crack within a few hours, whereas MABS may last much longer or may not crack at all.
2.2 Resistance to Stress Cracking: MABS Toughness Is the Key Difference
SAN is an amorphous, brittle material with a notched impact strength typically between 15 and 30 J/m. It is highly sensitive to stress concentrations at sharp corners, snap-fits, screw bosses, and weld lines. When residual stress after injection molding is slightly high, the part can easily crack during dropping, assembly, or solvent contact.
MABS is toughened by introducing a butadiene rubber phase, enabling a notched impact strength of 150-400 J/m, more than ten times that of SAN. This improvement in toughness gives MABS excellent performance in structural transparent parts, especially transparent housings with snap-fits, screw bosses, or hinges.
Typical Examples:
A transparent SAN cosmetic box cracks or even breaks when dropped from a height of 0.8 m;
- A transparent SAN cosmetic box cracks or even breaks when dropped from a height of 0.8 m; After switching to MABS, it passes a 1.2 m drop test and the yield improves significantly.
- A transparent SAN medication cup for a medical nebulizer develops stress cracks within several days after being wiped with 75% alcohol; After switching to MABS, the cracking problem is largely resolved.
2.3 Controlling Internal Stress During Injection Molding
Whether SAN or MABS is selected, internal stress must be controlled during processing:
- Appropriately increase the mold temperature (60-80°C recommended for SAN and 50-70°C for MABS);
- Avoid excessive injection pressure and holding pressure;
- Avoid sharp corners and abrupt changes in cross-section in the product design;
- Perform annealing when necessary (for example, anneal for 2-4 hours in a hot-air circulation oven at 70-80°C).
Because MABS has better toughness, it tolerates fluctuations in processing parameters better than SAN. However, SAN carries a very high risk of cracking if processed improperly.
3. Compliance for Medical and Consumer Products
3.1 Medical Industry Compliance Requirements
Medical devices and consumables impose strict biocompatibility requirements on materials and generally need to comply with the ISO 10993 series of standards. Some MABS and SAN grades can pass tests such as cytotoxicity and skin irritation, but not all grades have medical-grade certification.
Before selecting a material, medical customers must confirm:
Whether the grade has been tested according to ISO 10993 and whether the corresponding reports are available;
Whether it is compatible with the intended sterilization method:
| Sterilization method | SAN | MABS |
| Ethylene oxide (EtO) | Compatible | Compatible |
| Gamma radiation | Possible yellowing; a radiation-stabilized grade is required | Possible yellowing; a radiation-stabilized grade is required |
| Steam sterilization (121°C) | Not compatible; deformation will occur | Not compatible; deformation will occur |
Change management and batch traceability: Medical customers have strict requirements, and suppliers must provide a stable grade and a commitment to batch-to-batch consistency.
Important reminder: Do not assume that “transparent” means “suitable for medical use.” Medical-grade MABS and SAN usually cost more than general-purpose injection-molding grades and have limited sources of supply. If your product is a medical device or a consumable that comes into contact with the human body, inform the supplier in advance so that the correct grade can be selected.
3.2 Consumer Product Compliance Requirements
Compliance requirements for consumer products are relatively flexible and mainly focus on:
FDA food contact: SAN is widely used in transparent food-contact parts, such as blender jars, viewing windows for food containers, and transparent kettle housings. Some SAN grades comply with FDA 21 CFR requirements. Food-contact grades of MABS are also available, but they are less common and the selection is more limited.
REACH / RoHS: Conventional SAN and MABS grades generally comply, but grades containing flame retardants or other additives must be confirmed separately.
Toy safety: EN 71 and ASTM F963 specify mechanical and physical requirements for toys. The high toughness of MABS makes it more suitable for transparent toy parts that may be dropped by children. When SAN is used for transparent toy parts, particular attention must be paid to drop and bite tests.
3.3 Compliance Documentation Support
Reputable plastic raw material suppliers can generally provide:
- TDS (Technical Data Sheet)
- SDS/MSDS (Safety Data Sheet)
- REACH declaration
- RoHS report
- FDA declaration (if applicable)
- ISO 10993 report (if applicable)
Before introducing a new material, manufacturers are advised to request a complete set of compliance documents from the supplier and retain them on file to avoid problems during subsequent audits.
4. Cost and Substitution Recommendations
4.1 Price Positioning
MABS is typically 30%-50% more expensive than SAN but less expensive than PC. It is a highly cost-effective option among transparent, tough materials.
SAN has a low price, good flowability, and a wide processing window. It is suitable for high-volume, low-load transparent parts with demanding appearance requirements.
Key reminder: Material price is only one part of the total cost. If SAN products have a high scrap rate due to cracking during production or generate many after-sales returns, their total cost may actually be higher than that of MABS. Likewise, if the toughness of MABS far exceeds the product’s requirements, using SAN can significantly reduce the cost per part.
4.2 When Can SAN Replace MABS?
The product is not subjected to impact loads, or its wall thickness is sufficient (>2.5 mm) to withstand ordinary external forces;
The service environment contains no aggressive chemicals, and the product is not frequently dropped;
Typical applications: transparent display boxes, stationery, rulers, cosmetic trays, and non-load-bearing transparent decorative parts.
4.3 When Should MABS Replace SAN / PS / PMMA / PC?
SAN/PS parts frequently crack or fail drop tests → switch to MABS;
PMMA is too brittle and lacks sufficient heat resistance → MABS balances toughness and transparency;
PC is too expensive, but the product requires a certain level of toughness → use MABS as an intermediate option;
For transparent parts requiring structural features such as snap-fits and screw bosses, SAN/PMMA can crack easily, while MABS is more reliable.
4.4 Recommended Substitution Validation Process
If you are considering a material substitution, the following steps are recommended:
Confirm differences in MFI and molding shrinkage for the target grade, and assess whether mold adjustments are required;
Conduct a small-batch mold trial, focusing on drop performance, chemical resistance, appearance, and assembly;
Measure critical dimensions and fine-tune the mold shrinkage allowance if necessary;
Make the formal switch only after confirming that all compliance documents are complete.
Conclusion
Neither SAN nor MABS is absolutely superior; the key consideration is whether the product faces impact or cracking risks. If your transparent part is only used for static display and bears no load, SAN is an economical and efficient choice. If the part has snap-fits or screw bosses, may be dropped, or comes into contact with disinfectants or cosmetics, the toughness advantage of MABS can greatly reduce after-sales risks.
If you are deciding between SAN and MABS, please provide your product drawings, application environment, and test requirements. We can help you select a specific grade and provide a TDS comparison table, compliance documents, and sample support.
