Resin Tray PDMS Thickness and PDMS alternatives


I am using the Form2 printer with a custom resin for research. Unfortunately, the resin is incompatible with the PDMS in the resin tank as it caused it to swell and separate from the tank. I am now looking for alternative materials to use in my resin tank after taking out the PDMS.

Does anyone know the thickness of the PDMS placed within the resin tank? If I am going to replace the PDMS I need to be close to matching the thickness as the z-fine tuning can only be adjusted +/- 2 mm.

Additionally, has there been any success with using another material besides PDMS at the bottom of the resin tank? I have read a few topics where people have used another silicone, but I worry that those too will swell. Ideally, I would like to use a glass or plastic, but I worry those will distort the laser.

Thanks for your time and assistance.

Sylgard 184 is the silicon of choice to replace the worn out PDMS. Not sure of the amount, but someone had mentioned it on the forum somewhere.

keep an eye on the other thread by billie that she is working on putting FEP on top of the PDMS layer… You can buy FEP with adhesive backing and put it right on top of the PDMS. this should work for you just fine by creating a barrier against your resin hitting the PDMS, but still giving you good squish and results

I have used the slygard 184 on both the form 1+ and Form 2 trays without issue. I have found that if I weigh the PDMS layer after peeling it out of the tray and replacing with the same weight in slygard 184 it works well. I have re-coated several trays multiple times. I have found that after 3 to 4 re-coats the plastic at the bottom of the trays is getting a few scratches from the many cleanings. I am not overlay cautious when I replace the PDMS layer so if you are careful you might get 5 or more re-coats before you need to trash the tank and start with a new one.
Scout Design & MFG

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Just caliper the material after you’ve removed it to get it’s thickness (but it’ll vary depending upon where in the tray it was).

You’ll also probably want to weigh it, compare your PDMS replacement weight to that of sylgard 184, and figure out how much by weight to pour in.

@ZVat_Industries can probably help you out. See his website and ask him about PDMS alternatives. He’ll know if anyone would. I have two of his Form1 glass-bottom vats and they are outstanding.

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anyone tried this (or think it might be appropriate?)

If the custom resin caused the PDMS to swell, any replacement silicone you put in will also likely swell. I’d look into some of the other options suggested in this thread.

I would recommend checking this thread for ideas too. It is currently highly active, and the previous thread had some good suggestions.


I am going to try an FEP film over the PDMS. This worked in the thread here when placed over a portion of the PDMS. Enhancing the life of the resin tanks. CONT

I’ll update how it goes.

The FEP film I will try is here.


Good luck. Good tips in that thread

Jason, I actually have a Gallon of that material here,(Different Brand (Industrial Polymers) but the same stuff) Used to simulate water. I was going to try it on an old tank, But since it is a Urethane based material I think it will cause some problems especially with sticking to much… It doesn’t have “Slick” Properties like silicone does so you are just relying on the smoothness and I think the Resin will bond to it. Now as a base to apply a FEP sheet over the top of it would work as the FEP would stick like no tomorrow to the urethane and you would have a soft underlayment, But at that price it really is not any savings over the 184 Silicone.

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or theres this stuff -

Just finished re-coating our vats. I am seeing 102-103 grams of PDMS on our OEM vats from Form. Hopefully this helps!

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Did you notice any “waviness” to the FEP? Mine appeared to come like that. Additionally, any suggestions for taking the FEP off and putting it down without creating bubbles or crinkles? I just got mine in today and was having some issues using it.

When I used a longer sheet I started it on the side of the tank where I know I could get a good Bite then just slow worked it down onto the PDMS with my thumb going back and forth across while peeling the back.
No doubt it is a pain in the rear… What you can do to help keep the FEP from stretching is to cover the top side with masking tape apply the fep then take off the masking tape… This is how we apply vinyl to signs by using what is called a Premask. It holds all the letters in place so we can apply them to the metal then pull off the mask once stuck. down.

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Hey, I have an update. We have now applied the FEP film to our resin tray and we have found that our resin will cure through the film. However, we are now experiencing trouble getting the resin to actually stick to the build platform and we find some resin stuck to the film on the resin tray, indicating that we are able to cure the resin.

So far, we have tried moving the platform down 0.5 mm, but no luck. We are going to try going even lower. Can going too low potentially cause a printing failure? Our parts we are trying to make are with the supports, and I have filtered the resin through some paint strainers. Could cloudiness affect adhesion, and is there any way in reducing cloudiness? Our material isn’t clear, but neither are most of the resins from Formlabs.

Any other suggestions for increasing adhesion to the build platform? I appreciate any help provided.

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Depends on what color resin you are using.
The FEP is only about 85% transparent (or so) so you need to actually cure a bit longer with FEP than PDMS, so perhaps a profile with a longer cure time.

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I noticed that the tough resin has a longer print time for the same material at the same layer height, is it known that this cures longer per layer? I might give that a shot. Looking through, it seems like all the other reins take about the same amount of time. Or is there a way to program the machine to cure longer?

We are gonna have a DIY PDMS refill kit for you guys very soon. Should be like $15-$20 and it will fill a vat to the correct level. Super easy!
{oops, had the wrong price earlier}

If anyone wants more info you can email us at…but we will post here as well when things are ready.


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Here’s another 12"x12" square of opticall clear FEP tape

It’s double mcmaster’s price, but it might be a worthwhile datapoint to try it.