Frequently Asked Questions

  • What types of silicone does Elkem offer for use in healthcare/medical device manufacturing?
    → Liquid Silicone Rubber (LSR)
    → Heat Cure Rubber/High Consistency Rubber (HCR)
    → Room Temperature Vulcanizing (RTVs)
    → Silicone Gels
    → Soft Skin Adhesives (SSAs)
    → Elastomer Dispersions
    → Adhesives
    → Dimethylpolysiloxane Fluids


  • What is the difference between Gel, RTV, LSR, & HCR?
    → Below is a chart comparing some common properties/processing conditions that can help in selecting a type of elastomer for an application:





No reinforcement

Silica reinforced

Mixed viscosity (cps)

3k – 45k

5k – 300k

100k – 150k
thick paste



2 component

2 component or

1 component (chemistry dependent)

2 component

2 component or

1 component (chemistry dependent)

Cure Chemistry

Optimal Cure Temperature

Room temp or

 50˚C – 120˚C

Room temp or

50˚C – 120˚C

110˚C – 200˚C

300˚C – 350 ˚C

Durometer Range

Penetration: 3 – 25 mm

5 ShA – 50 ShA

1 ShA – 70 ShA

20 ShA – 70 ShA

Process technologies

Coatings, Pouring, Encapsulated,

Pouring/casting, coating

Injection molding, coating

Extrusion/calendaring injection molding


  •  Polyaddition CureWhat does polyaddition cure mean?
    → Polyaddition cure is the most common cure mechanism used in medical grade silicone elastomers. These are two component platinum catalyzed silicones. At Elkem, part A contains vinyl functional polymer(s) and the platinum catalyst. Part B component contains the hydride crosslinker and inhibitor. In the presence of platinum the hydride and vinyl functionalities will react to form a cured silicone elastomer.



  •   Why are some medical silicone parts post baked/post cured?
    A typical post curing process is 2-4 hours at 200˚C. Post curing is sometimes undergone to remove any remaining volatiles to meet certain FDA and BGVV guidelines. In general polyaddition cured silicone elastomers will lose < 0.3 wt% of volatiles during a post cure cycle.
    → Elkem Silicones LSR 43xx Series products were designed to give high strength, stable physical properties without the need for post curing. Some elastomers, such as older generations of Elkem LSRs, may make use of a post cure to achieve higher physical properties.


  • What is the shrinkage of Elkem’s LSR and HCR molded parts?
    Linear shrinkage of parts molded with Silbione® LSR is typically 1.5 – 2.5%.  Exact shrinkage depends on:
    → chemical formulation of the Silbione® LSR or HCR
    → molding temperature
    → cavity pressure
    → where the shrinkage measurement is made (shrinkage is usually slightly higher in the direction of the material flow than perpendicular to the direction of flow).
    → dimension of the part (thicker parts shrink less than thinner parts)
    → post curing causes an additional 0.3 – 0.5% shrinkage.


  •  How to sterilize silicone molded parts?
    Sterilization methods for medical devices include steam sterilization, ethylene oxide, electron beam, and gamma radiation. While these processes are necessary for sanitizing purposes, they can affect the molecular structure of the silicone rubber resulting in adverse effects on the physical properties of the molded part.

    Ethylene oxide (EtO) treatment
    has no significant negative effect on elastomers but residual EtO gas can be absorbed by the silicone rubber upon prolonged exposure.Generally, steam sterilization (steam autoclaving) at 120°C – 130°C can be carried out continuously for most LSR grades. Silicone rubber behavior in steam is not uniform for all grades of elastomers.At temperatures approximately 212°C and greater, oxidative degradation begins to occur. Thus, shrinkage of the molded part is evident along with an increase in hardness and embrittlement.The effects of electron-beam and gamma radiation are comparable to the effects of exposure to high temperatures.  Generally a 2.5 Mega-Rad dose of gamma irradiation will have < + 15% effect on physical properties of most Silbione® LSR and HCRs.  Testing of the actual molded article should be conducted to confirm effects of the gamma or electron irradiation and final fitness for use.


  • What is the life time of a cured silicone elastomer part?
    Elkem Silicones does not test the shelf life of cured silicones nor does it provide the certification for cured silicones shelf life. However, based on the data found in literature, the typical shelf life of injection molded silicone is more than 20 years if product is properly stored.  Proper storage would include ambient temperature and humidity, in a sealed bag out of direct exposure to sunlight.


  • What makes a silicone product medical grade?
    The manufacturing conditions, quality of raw materials, biocompatibility testing and regulatory support of a particular grade makes it medical vs. industrial grade. Elkem’s Silbione® grade products are supported for use in medical, skin contact, food contact, and/or short term (<29day) implantable applications. Products in the Silbione family are manufactured in a clean environment with the strictest regimen of regulatory & quality control. Minimally all Silbione® products have passed testing for cytotoxicity, sensitization (allergy), and skin irritation. See technical data sheets for all USP Class VI and ISO 10993 testing information.


  • What temperature range is silicone stable?
    → Thermal stable from -60˚F to 500˚F (-50°C to 250°C)
    → The Si-O bond of silicone elastomers makes it thermally stable. Note while silicone is stable at these temperature physical properties of products will be affected when exposed to the extremes for a length of time.


  • How do you remove cured silicone from surfaces?
    → Several solvents can be utilized to remove cured silicone elastomer from surfaces:
    → D4 or D5, Xylene, isopropyl alcohol