--- title: Explaining Shrink in Silicone Injection Molding | Extreme Molding description: Shrink is a common issue in all injection molding processes, both silicone and plastic. As long as you are working with a skilled manufacturer, who has ample knowledge in material science, they should know how to account for the shrink in your design. Here's a look at common issues and how to avoid them. image: https://www.extrememolding.com/hubfs/Imported_Blog_Media/Sink-marks-on-silicone-injection-mold.png --- [![Extreme Molding Silicone Injection Molding](https://www.extrememolding.com/hs-fs/hubfs/Extreme-Molding-logo-web.png?width=300&height=85&name=Extreme-Molding-logo-web.png "Extreme Molding Silicone Injection Molding")](https://www.extrememolding.com) - [FAQ](https://www.extrememolding.com/faq) - [Blog](https://www.extrememolding.com/blog) - [Ebooks](https://www.extrememolding.com/ebooks) - [Contact](https://www.extrememolding.com/contact) - - - Menu - [Home](https://www.extrememolding.com) - [Our Services](https://www.extrememolding.com/our-services) - [Silicone Injection Molding](https://www.extrememolding.com/injection-molding) - [Packaging & Fulfillment](https://www.extrememolding.com/packaging-fulfillment) - [Overmolding](https://www.extrememolding.com/overmolding) - [Color Matching](https://www.extrememolding.com/color-matching) - [Compression and Transfer Molding](https://www.extrememolding.com/compression-transfer-molding) - [Value Added Secondary Operations](https://www.extrememolding.com/value-added-secondary-operations) - [Our Markets](https://www.extrememolding.com/our-markets) - [Consumer Products](https://www.extrememolding.com/consumer-products) - [Female Healthcare Products](https://www.extrememolding.com/female-healthcare-products) - [Healthcare Products](https://www.extrememolding.com/healthcare-products) - [Infant Healthcare Products](https://www.extrememolding.com/infant-healthcare-products) - [Pet Products](https://www.extrememolding.com/pet-products) - [Promotional Products](https://www.extrememolding.com/promotional-products) - [Capabilities](https://www.extrememolding.com/capabilities) - [About](https://www.extrememolding.com/about) - [Careers](https://www.extrememolding.com/careers) - [Our Team](https://www.extrememolding.com/our-team) - [Our Process](https://www.extrememolding.com/our-process) - [Sustainability](https://www.extrememolding.com/sustainability) - [Testimonials](https://www.extrememolding.com/testimonials) - [Free Consultation](https://www.extrememolding.com/free-consultation) # Explaining Shrink in Silicone Injection Molding ![Sink marks on silicone injection mold](https://www.extrememolding.com/hs-fs/hubfs/Imported_Blog_Media/Sink-marks-on-silicone-injection-mold.png?width=370&height=329&name=Sink-marks-on-silicone-injection-mold.png "Sink marks on silicone injection mold")   Shrink is a common issue in all injection molding processes, both silicone and plastic. As long as you are working with a skilled manufacturer, who has ample knowledge in material science, they should know how to account for the shrink in your design. Silicone shrinks more predictably than plastic, so it is easier to account for. All plastic resins have different shrink rates, and they are much larger than the shrink rates of silicone. Plastic shrink can also result in sink, which can be a large problem atheistically. Shrink is always accounted for in mold design. The manufacturer increases the cavity to be 1-4% larger than the desired part, based on the material data sheets and the shrink rate. When the product cools or cures in the mold, it will begin shrinking. Shrinking will continue to happen to the part for the next 24 hours. If you are ever doing measurements on critical dimensions of a part, it should wait until 24 hours after molding. ### **Plastic Shrink & Sink** Plastic resins can shrink anywhere from 1-4% of its size after molding. Therefore, it is important to build the shrink into the mold design. Different wall thicknesses will shrink at different rates, and this is where sink come in to the equation. Sink happens on a plastic part when the part is too thick in areas. It is important to thin these areas out and create equal wall thickness throughout the part. Sink marks will look like a divot in the part on the thick areas. Shrink happens while the part is cooling, and when the area is very thick, it takes a much longer time to cool, causing excessive shrink to happen in that area. Using an experienced molder, they will be able to flag situations like this and help you design for manufacturability. ### **Silicone Shrink** All silicone shrinks at approximately the same rate; therefore, it can be more predictable. The shrink is simply built into the mold design. Even though sink is not much of a problem, we still must watch out for thick wall parts in silicone. Thick wall parts can result is under-cured parts, deforming or backrind. - **Undercured**: Thick silicone parts will take a long time to cure, so when it is removed from the mold, it may still be soft and uncured on the inside. This will result in post baking. - **Deformed**: While the thick part is still uncured on the inside, it may become deformed during removal from the tool, or while the part cured outside of the mold. - **Backrind**: If we attempt to increase the cure time inside the tool to finish the cure instead of post baking, the silicone part will begin to expand under the heat. This causes the material to press up against the sides of the tools and rip at the parting line. This is call backrind. This can be a difficult idea to grasp, but one that any silicone molder is well versed in. These common shrink issues are avoidable by partnering with a skilled manufacturer who are ample knowledge in material science. Partnering with the right manufacturer will help your components turn out right the first time, reducing production times and costs. If you’re looking for a manufacturer for your injection molded components, [contact us](https://www.extrememolding.com/contact-us) today. ###### Watch our video to learn more about our Packaging and Fulfillment Services ###### Have an idea for a product? Do you have a great idea for a US manufactured product? We can help bring it to life. From advising you through the injection molding process, to delivering your new product to customers, we want to work with you every step of the way. Contact us to learn more. [Contact Us](https://www.extrememolding.com/contact) July 30, 2018 | Tags: - [Product Design](https://www.extrememolding.com/blog/tag/product-design), - [Silicone Shrink](https://www.extrememolding.com/blog/tag/silicone-shrink), - [Injection Molding](https://www.extrememolding.com/blog/tag/injection-molding), - [Molding](https://www.extrememolding.com/blog/tag/molding), ##### Share This Story, Choose Your Platform! - - - - [mailto:info@example.com?&subject=Explaining%20Shrink%20in%20Silicone%20Injection%20Molding%20|%20Extreme%20Molding&cc=&bcc=&body=](mailto:info@example.com?&subject=Explaining%20Shrink%20in%20Silicone%20Injection%20Molding%20|%20Extreme%20Molding&cc=&bcc=&body=) ###### Related Posts ##### [Silicone Casting vs Injection Molding: Which One Is Right for You?](https://www.extrememolding.com/blog/silicone-casting-vs-injection-molding) August 19, 2026 ##### [Innovations in Medical Silicone Molding in 2025](https://www.extrememolding.com/blog/innovations-in-medical-silicone-molding) March 4, 2025 ##### [Injection Molding Is Ideally Suited for Medical Components: Here’s Why](https://www.extrememolding.com/blog/injection-molding-is-ideally-suited-for-medical-components-heres-why) February 13, 2025 ###### Categories - [Product Design](https://www.extrememolding.com/blog/tag/product-design) - [Silicone Shrink](https://www.extrememolding.com/blog/tag/silicone-shrink) - [Injection Molding](https://www.extrememolding.com/blog/tag/injection-molding) - [Molding](https://www.extrememolding.com/blog/tag/molding) ###### Recent Posts - [Silicone Elastomers for Medical Products](https://www.extrememolding.com/blog/silicone-elastomers-for-medical-products) - [Silicone Casting vs Injection Molding: Which One Is Right for You?](https://www.extrememolding.com/blog/silicone-casting-vs-injection-molding) - [Why FDA Regulations Matter in Medical Silicone Manufacturing](https://www.extrememolding.com/blog/why-fda-regulations-matter-in-medical-silicone-manufacturing) - [Your Baby's Pacifier Might Not Be What You Think It Is](https://www.extrememolding.com/blog/your-babys-pacifier-might-not-be-what-you-think-it-is) - [Guide to Safe Baby Product Manufacturing in the USA](https://www.extrememolding.com/blog/safe-baby-product-manufacturing-in-usa) - [Silicone vs Plastic for Your Dog Bowl: What Material Should You Choose For Your Product?](https://www.extrememolding.com/blog/silicone-vs-plastic-dog-bowl) - [LSR 2025 Insights + How Tariffs Impact Manufacturing](https://www.extrememolding.com/blog/lsr-2025-insights-how-tariffs-impact-manufacturing) - [Two-Shot Molding vs. Overmolding: What’s the Difference?](https://www.extrememolding.com/blog/two-shot-molding-vs-overmolding) - [From Breast Pumps to Nursing Pads: Why Silicone Is Ideal for Women’s Healthcare Products](https://www.extrememolding.com/blog/from-breast-pumps-to-nursing-pads-why-silicone-is-ideal) - [White Room vs. Clean Room Manufacturing: Key Differences](https://www.extrememolding.com/blog/white-rooms-vs-clean-room-manufacturing-key-differences) [Read More](https://www.extrememolding.com/blog) [![Extreme-Molding-logo-web](https://www.extrememolding.com/hs-fs/hubfs/ExtremeMolding-theme-2023/images/Extreme-Molding-logo-web.png?width=300&height=85&name=Extreme-Molding-logo-web.png "Extreme-Molding-logo-web")](https://www.extrememolding.com) Extreme Molding is a unique silicone molding company formed in 2002 outside Albany, N.Y. 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