SLS Refresh Rate: What is it, and how does it work?

What is SLS refresh rate?


The SLS refresh rate is the percentage of the new cartridge that is ‘refreshed’ with new, unused powder, with the remainder made up of recycled powder. For example, 30% recycled powder means a 70% refresh rate.




The Formlabs Fuse 1 makes highly complex and intricate parts with unique geometries, using a high-powered laser to selectively ‘sinter’ nylon powder instead of a mechanical print head in FFF or a laser resin curing system in SLA.


One of the biggest advantages to SLS with the Fuse 1 is powder recovery, which significantly reduces waste. This is known as refresh rate.


To recover powder, you need the Fuse Sift (available separately and with the Fuse 1 as part of the High-Efficiency Package), a powder recovery system that extracts, recovers, stores, and mixes nylon powder to reduce waste.





The Fuse 1 prints a mixture of virgin and recycled powder from previous prints. This lowers the cost per part without sacrificing print quality.


How does refresh rate work?


When the Fuse 1 prints nylon powder, unsintered powder escapes the final model and gets collected, the Fuse Sift, a separate but integrated device, extracts that material and recycles it, effectively recovering otherwise ‘wasted’ powder.


To use the Fuse Sift, you load the Fuse 1’s build chamber into the Fuse Sift for a contained and efficient workflow. The Fuse Sift then sifts powder from the build chamber, collecting all unsintered powder with a refresh rate of around 30%.


The packing density, or how closely parts are arranged in the build chamber, affects how much powder is left unsintered.


Recommended refresh rates


Formlabs recommends refresh rates for different materials, giving you benchmarks to work with for high-quality, consistent models and parts.


Here’s a graphic illustrating those refresh rates:


Refresh rate SLS


While it is not advisable to use 100% recycled powder (0% refresh rate), you can print with a refresh rate of 30% with a deviation of 10%.


Different materials have different recommended refresh rates because recycled materials lose some structural quality during processing. Therefore, fresh powder is required to make up the bulk of new parts.

Summing up


Refresh rate is the amount of new powder used in cartridges. For instance, a 70% refresh rate means cartridges contain 30% recycled powder.


The Fuse 1 and Fuse Sift automate the process of powder recovery, creating an all-in-one workflow that maximises recycling rates.

Find out more


To find out more about the Fuse 1, request a Formlabs sample, call us on 01765 694 007, or send us an email at


You can also book a discovery call with our Formlabs specialists Elaine Rutledge or Tammy O’Neill.


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