It's fairly common for E3D to sell silicone socks for their hot ends. There are also other companies that sell these silicone socks for their hot end cartridges.

According to a brief internet search, it seems the ignition temperature of silicone is surprisingly low - around 450 °C. This surprised me because I was under the impression silicone would just burn / evaporate if it were heated up to a much higher temperature.

If my thermistor/heatrod slips off, my heatrod will glow into an orange temperature during thermal runway. This only happens briefly, but its color indicates it is reaching a temperature around 790 °C.

So, are silicone socks safe? Couldn't they ignite fairly easily?

Incandescence chart for iron

  • 12
    $\begingroup$ The more pressing issue here is not whether the sock will ignite, it's why your heater is reaching 800 °C in the first place. This should almost never happen under any circumstances in normal operation, as the upper limit for printing temperature on most common materials is 280 °C. Either your thermal-runaway protection is not sufficient in any way, or you're pumping WAY too much energy into your hotend. $\endgroup$
    – craftxbox
    Commented Nov 19, 2019 at 3:54
  • 5
    $\begingroup$ You are linking to a printer that had no Thermal Runaway Protection enabled. It seems that your printer doesn't either, please fix that first! $\endgroup$
    – 0scar
    Commented Nov 19, 2019 at 7:09
  • 5
    $\begingroup$ note that your Incandescence chart is technically the iron one, the one for aluminum is a little different (by a margin of some hundred degrees). Note that Aluminium (which your heater block is made of) melts at 660 °C, so your most worrying item should be the block, which will melt, drip and melt anything below if this goes on for a couple seconds like seen here $\endgroup$
    – Trish
    Commented Nov 19, 2019 at 10:23
  • 1
    $\begingroup$ Just as a by-the-way: there are heat resistant silicones that will burn very slowly and retard fires even if you cross into the high temperatures. Here is an example (Disclaimer, I have worked for the company who made this ad) youtube.com/watch?v=-xcxDTNbzho $\endgroup$
    – Stian
    Commented Nov 19, 2019 at 13:38
  • 2
    $\begingroup$ While it is good fire safety practice to keep around as few inflammable material as possible, don't forget that the usual filaments are flammable, too. Ultimater lists an ignition temp for their PLA of 388 °C and thermal decomposition from 250 °C (ultimaker.com/download/74613/…) $\endgroup$ Commented Nov 19, 2019 at 14:53

2 Answers 2


Neither your thermistor nor your heater cartridge should ever be capable of becoming loose from your hotend, let alone the fact it's capable of reaching 800 °C before your printer even notices (This is a massive issue in itself!!!)

Silicone socks are safe, unless you're printing materials with extremely high melting points, which is usually never.

If you're concerned it's going to autoignite mid-print, you have much bigger issues surrounding your hotend than a silicone sock.

  • 3
    $\begingroup$ @steveantwan it's not opinion based but PLEASE replace your firmware for one with TRP. $\endgroup$
    – Trish
    Commented Nov 19, 2019 at 10:15

Silicone socks are safe to use, provided your printer is safely operating and you are using the silicone socks in their operating temperature range.

Your current setup is NOT SAFE!

When the heater element falls out of the heater block (that should not happen in the first place, please secure it correctly) and heats up to about 800 °C this means that the printer has no active Thermal Runaway Protection (TRP) enabled. Basically, when the thermistor doesn't measure a temperature rise while the voltage to the heater element is being scheduled, the firmware should shut down the voltage to the heater element. When this fails, the heater element can reach dangerously high temperatures to start burning anything that can catch a flame on touch. In deliberate tests, heaters have been able to melt the aluminium of the hotend:

You should be worried at this point as you see from the link you provided what happens if the heater is not shut off when the heater element is disconnected from the heater block:

Burnt Anet A8 as a result of inactive TRP and heater cartridge falling out of the heater block

Please fix your printer ASAP by uploading a proper firmware with enabled TRP protection before proceeding to print anything or at least don't let it print without supervision and proper smoke/fire detection devices.


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