Polyurethane and silicone are both commonly used thermosetting polymers, which can be applied in fields such as sealing and shock absorption, as well as medical and health care. This article will attempt to explain and outline the differences between silicone and polyurethane, their specific uses, and why both products are equally important.
Silicone vs PU: Advantages And Disadvantages of Materials
Advantages of Silicone
- UV-resistant
- Non-toxic and with good biocompatibility
- Stable chemical properties
- The temperature resistance range is wide, from -50℃ to 200℃
- Electrical insulation
Disadvantages of Silicone
- High production cost
- Easy to attract dust
- The wear resistance is average
Advantages of Polyurethane
- Good wear resistance
- Low cost
- The processing technology is flexible
- Good adhesion
Disadvantages of Polyurethane
- Poor weather resistance
- The temperature resistance range is narrow, from -20℃ to 80℃
- Poor chemical resistance
Silicone vs PU: Physical Properties
Hardness
Hardness of Silicone
The hardness of silicone rubber is concentrated in the Shore A range, commonly ranging from 10A to 90A. 10A is as soft as rubber gloves and can be used as a silicone gasket or a sealing component. 90A is relatively hard and can be used as a structural support component. The overall texture is relatively soft and elastic, meeting the requirements of ergonomic design.
Hardness of PU
The hardness range of polyurethane is wider, from 35A on the Shore scale to 70D. 35A is soft and close to the lower end of silicone, while 70D is already hard and similar to plastic. It can be used to make both soft PU sealing rings and hard protective housings.
Flexibility
Silicone has strong resilience and can quickly return to its shape after repeated bending. It is very suitable for making components that need to move frequently, such as silicone buttons.
The hardness adjustment range of polyurethane is wide, ranging from soft to hard. It has outstanding tear resistance and performs stably in static or low-frequency bending scenarios, such as anti-slip layers and cushioning pads. However, its fatigue resistance is slightly weaker. After frequent and large-angle bending, fine cracks may occur.
Viscosity
- Silicone has a low inherent adhesiveness. When making keys or silicone rubber sealing rings, they are not prone to adhesion after being pressed together with plastic casings and metal brackets, and are convenient for disassembly, assembly, and maintenance.
- However, if you want the silicone to bond strongly with other materials, such as fixing a silicone strip to a rubber base, you need to treat the bottom surface separately; otherwise, it is prone to delamination.
- Polyurethane molecules have high inherent adhesive advantages. When polyurethane is used as a handle or seal, the peel strength is stable after being pressed together with nylon or ABS shells, and no additional glue is needed.
Transparency And Opacity
Silica gel itself has high light transmittance, translucent to transparent in the natural state, and good light transmittance uniformity.
The opacity of silica gel can be achieved by adding fillers and other methods.
Polyurethane has a wide range of transparency. You can make both the transparent type close to glass and the milky white semi-transparent type.
Density And Weight
The density of silica gel is concentrated between 1.04 and 1.12g/cm³, and the material itself has stable structural characteristics. The density of polyurethane elastomers varies greatly, typically ranging from 0.01 to 1.25g/cm³, enabling continuous coverage from ultra-light foaming to a highly dense state.
If you are pursuing a lightweight design, the polyurethane foam structure can significantly reduce the overall weight while ensuring mechanical properties.
Electrical Insulation
Silicone itself is a high insulator. The surface resistivity remains stable in a humid environment, and the insulation performance will not decline due to water vapor penetration.
Polyurethane is also an insulator in its initial state, but its molecular chain contains polar groups and is prone to adsorbing moisture from the air. After absorbing water, the electrical insulation of PU will decline.
Wear Resistance
Dynamic friction loss: Silicone has good elasticity. When you make buttons or wheels, it is not easy to have burrs when repeatedly pressing and sliding. However, under high-frequency and high-speed friction, such as industrial pulleys, they will gradually wear out and become thinner over long-term use.
The hardness of polyurethane is adjustable. When used as tool handles or conveyor belt rollers, they offer longer wear resistance and a longer service life.
Static wear resistance test: Silicone is under long-term static pressure, such as in sealing gaskets, and the edges are prone to cracking due to stress concentration. Polyurethane has strong tear resistance and maintains a more stable shape under static conditions. When used as equipment seals or as the interlayer of shoe soles, it is less likely to deform or wear out due to compression.
Heat Resistance
Silicone has a melting point of 250℃ and can maintain its shape without softening or decomposing even in an environment of 150℃ for a long time. You produce industrial equipment seals and outdoor high-temperature tool handles. They can withstand continuous heat loads and reduce the after-sales risk of failure due to high temperatures.
The melting point of polyurethane is only 80℃. If the temperature exceeds this, it will soften easily and decompose slowly when exposed to heat for a long time. Suitable for normal or low-temperature scenarios, such as the buttons of ordinary household appliances.
Silicone vs PU: Chemical Properties
Silicone vs PU: Waterproof Capability
The silicon-oxygen bonds in the main chain of silicone are dense, and its surface water vapor permeability is low. Even after long-term immersion in water or in a high-humidity environment, it still maintains its elasticity and does not expand.
Polyurethane has a loose structure and is prone to swelling after absorbing water. It may deform if used for a long time in a humid environment.
When you are making outdoor seals or kitchenware, the waterproof durability of silicone is more stable. For short-term waterproofing needs, polyurethane can also be used.
Silicone vs PU: Corrosion Resistance
Whether you choose silicone or polyurethane depends on its chemical resistance and compatibility with the application scenarios.
Silicone is resistant to high-temperature water erosion, salt water penetration, brake fluid corrosion, and contact with chlorinated hydrocarbons, making it suitable for components that need to withstand such media.
Polyurethane has good fuel resistance, oil resistance, solvent erosion resistance, and weak alkali and acid contact resistance, making it more stable for use as accessories in such scenarios.
Silicone vs PU: Weather Resistance
Silicone has a strong point in resisting ultraviolet rays. It won’t yellow or crack when used outdoors for several years. Polyurethane tends to turn yellow, and its surface may become hard if exposed to the sun for a long time.
If you are making outdoor equipment casings or car buttons, choosing silicone is more worry-free. For small accessories used indoors for a short period of time, polyurethane is sufficient due to its low cost.
Silicone vs PU: Application Difference Comparison
Application Scenarios of Silicone
Medical Devices
The biocompatibility of silicone is key. Catheters, infusion tubes, and implantable devices do not release harmful substances even when in direct contact with the human body.
Children’s Products
For entry-level products like baby pacifiers and teething rings, silicone is non-toxic, soft, and elastic, which makes parents more at ease.
Industrial Scenarios
Choose silicone for high-temperature sealing parts.
Electronic Devices
Silicone waterproof gaskets are resistant to cold and heat shock, protecting circuits from water ingress.
Kitchenware
baking molds, ice cube trays, chocolate molds, silicone, high-temperature resistant, and easy to demold.
Mold Manufacturing
It can be used to cast polyurethane products, with strong self-stability and high precision of finished products.
Application Scenarios of PU
Shoe Soles, Tires
You make shoe soles, skateboard wheels, and forklift tires. Polyurethane is wear-resistant and durable, which is an advantage. The sole of the shoe won’t harden or crack after walking ten thousand steps, and the wheels won’t burst when running over stones.
Impact Dampers for Railways And Elevators
Polyurethane energy-absorbing buffers to reduce equipment damage.
Industrial Pipe Lining
Polyurethane is resistant to acid and alkali corrosion and does not leak when transporting corrosive liquids.
Pump Impellers And Conveyor Belts
Polyurethane has better wear resistance than ordinary rubber, which extends the replacement cycle—chute lining, vibrating screen, polyurethane impact-resistant, not damaged by material friction.
Electrical Equipment Potting
Polyurethane can isolate water vapor and dust, protecting the stable operation of precision components.
How to Process Silicone And Polyurethane?
The Production Process of Silicone
Mold Opening Casting
If you are making complex-structured keys or medical catheters, choose mold casting. It can replicate fine patterns and is suitable for small-batch customization.
Compression Molding
For mass production, mold pressing is selected. After the silicone is mixed with the curing agent and filled into the mold, it is vulcanized under heat and pressure, which is highly efficient and dimensionally stable.
Injection Molding
For urgent orders or standardized parts, injection molding is used. The cycle is short, and it is suitable for large-scale mass production of electronic accessories.
The Production Process of Polyurethane
Rotary Casting
If you are making shoe soles or skateboard wheels, rotary casting is more suitable. When liquid polyurethane is injected into a rotating mold, the centrifugal force is evenly distributed, resulting in a high density and wear resistance of the finished product.
Reaction Injection Molding
For industrial pipe linings or complex shells, reaction injection molding is faster: after the raw materials are mixed, they solidify rapidly in the mold, making it suitable for one-time molding of thick-walled parts.
Polyurethane can also be classified into cold and hot curing types. If you need high mechanical properties (such as load-bearing wheels), choose the hot curing process. This way, the cross-linking is more complete and the tear resistance is stronger. Cold curing is used for common protective parts, which saves energy and shortens the delivery time.
Is There A Big Price Difference Between Silicone And Polyurethane?
The price stratification of silicone: RTV-1 silicone is relatively inexpensive and suitable for small-batch production of basic parts such as simple keys and gaskets. RTV-2 silicone is much more expensive. It has stronger elasticity and heat resistance. For high-demand products such as medical catheters and high-temperature equipment seals, it is the only choice to withstand the requirements.
The price difference of polyurethane: Cold-cast polyurethane is tear-resistant and has good load-bearing capacity. It is used to make wear-resistant parts such as skateboard wheels and industrial casters. Hot casting has a low cost and is suitable for making parts with low performance requirements, such as ordinary shoe soles and pipe linings.
Silicone vs PU: Safety And Environmental Friendliness
Silicone is naturally skin-friendly and non-toxic. Medical-grade silicone has passed the ISO 10993 biocompatibility certification and does not cause rejection when in direct contact with human tissues. Food-grade silicone meets FDA standards and can be used to make baby pacifiers and kitchen molds, which parents can use with peace of mind. The aging resistance also reduces the frequency of replacement and the generation of waste silicone.
Some types of polyurethane may contain trace amounts of VOCs (volatile organic compounds). When making indoor products, low-volatile formulas should be selected. However, it has strong compliance in the industrial field, has passed the EU REACH test, and is used for pipe linings and equipment seals, without contaminating the conveyed medium.
Can polyurethane And Silicone Be Recycled?
Both are thermosetting polymers. Once the maximum service temperature is exceeded, they will decompose into harmful chemicals and cannot be remelted like thermoplastics to make new parts.
At present, mechanical granulation is mainly relied on to grind the materials into small particles, which can only be used as filling materials and cannot be turned into virgin materials. Even if they are recycled, they cannot be regarded as truly sustainable materials.
When you make products, if you want to play the environmental protection card, you have to accept the limitations of this recycling.
Which One Comes Out on Top: Silicone or Polyurethane?
Determine The Application Requirements
First, consider where the product will be used – medical catheters sterilized at high temperatures? Or outdoor wear-resistant wheels? Different demands lead to different material directions.
Consider The Material Properties
Silicone has good compatibility with the human body, is safe, and resistant to heat, weather, and chemical corrosion . Polyurethane is wear-resistant and tear-resistant, making it more stable in load-bearing scenarios.
Evaluate Performance
Choose silicone for high-temperature environments; it does not deform at 200℃. For frequent friction, choose polyurethane for a longer lifespan.
Evaluate Lifespan
Silicone used in medical equipment should not be replaced for several years. Polyurethane for industrial casters wears out slowly and requires less maintenance.
Cost Analysis
Silicone may be a bit more expensive initially, but it should be replaced less frequently over the long term. Polyurethane is cheap, but frequent replacement will increase costs.
Sustainability And Environmental Impact
Both are difficult to recycle, but silicone is more likely to pass environmental protection certifications.
Regulatory Compliance
For food contact or medical products, the biocompatibility certification of silicone is more comprehensive.
Consult An Expert
If you need any other assistance, please feel free to contact Legensilico at any time. We are more than willing to help you sort out your thoughts and guide you in making a decision, so that you know which product is the most suitable for you.
Summary
There is no such thing as either silicone or polyurethane being better. It all depends on the scenario you want to apply it to. Ultimately, your decision is highly subjective. However, each manufacturer needs some advice when deciding whether to use silicone or nylon raw materials as part of the production process.
If you need any other suggestions, please feel free to contact Legensilicon at any time. We are more than willing to help you solve the problem.
FAQ
What Are The Alternative Materials for Polyurethane And Silicone?
- Alternative to silicone: TPE has balanced, comprehensive performance, with elasticity close to that of silicone. It does not require vulcanization during processing and can be directly injection molded. It is suitable for making basic parts such as keys and sealing rings, and its cost is 10% to 15% lower than that of silicone.
- Alternative to polyurethane: TPR has more outstanding low-temperature resistance. It is not hard or brittle in an environment of -30℃. It can be used as an alternative to polyurethane for shoe soles and skateboard wheels, making it more durable in winter.
TPU retains the high wear resistance of the original polyurethane and can replace industrial parts such as conveyor belts and pump impellers.
PU Sealant vs Silicone Sealant
Polyurethane Sealant
Advantages: Tough and tear-resistant, it can withstand salt spray from the seaside, oil stains from cars, and moisture from buildings.
Disadvantages: Poor UV resistance, prone to cracking after two years of outdoor use; The curing time is long, so a 3-5 day period should be reserved in advance for construction. There is also a pungent smell. After completion, ventilation is needed to disperse the odor, and cleaning is troublesome.
When it comes to sealing building curtain walls, automotive headlights, or Marine equipment, polyurethane has significant advantages
Silicone Sealant
Advantages: Weather-resistant, UV-resistant, and heat-resistant
Disadvantage: It cannot be painted. If you want to do a colored seal, you need to choose the colored one in advance. It will collapse when the temperature exceeds 200℃, and high-temperature equipment cannot be used. It does not bond firmly with some plastics (such as PP), and its compatibility is limited.
Suitable for roof waterproofing, sealing of electronic equipment cases, or pipes.
PU Leather vs Silicone Leather
The Advantages of Silicone Leather
- Silicone leather is wear-resistant and scratch-resistant.
- It has excellent water resistance. Water won’t seep into the backpack on rainy days, and it will be clean with just a wipe.
- It has better breathability than PU. When used as a sports bracelet strap, it won’t make you sweat in summer. It is eco-friendly, causes less production pollution, and only needs to be replaced after five years of use, which conforms to the current trend of consumers buying durable products.
Characteristics of Polyurethane Leather
- PU synthetic leather is relatively inexpensive. It is suitable for basic sofas and single-shoulder bags with high sales volume.
- However, it is less durable.
- The breathability is poor. When used as the inner lining of summer sandals, users have reported that it feels too warm on the feet.
- It also has weak environmental friendliness, with slightly higher pollution during the production process and a short life cycle.
For high-end products, if you want a good reputation, choose silicone. Durable, breathable, and environmentally friendly, users are willing to pay for durability. Mass market, choose PU. It has a low cost and covers essential scenarios such as furniture and bags.
