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Is spray foam / expanding foam safe for aquariums?

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I've gotten mixed results from my internet research, and some people say certain brands are safe while other brands are not. I'd like to do a 3d background with spray foam on my new ten gallon tank but I obviously do not want it to poison fish ... is spray foam safe? If so, which brand works best?

Thanks for the help!!!

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Just use care on not applying it too deep, it need moisture from the atmosphere to cure. For example, if you fill a PVC pipe with Great Stuff, the middle will not cure. I found out the hard way while making Harry Potter candles, fill the pipe then cut them down to size. What a mess that was.

What many do, after the foam cures you slice off the outer skin of the foam (silicone will not adhere to it) . Then cover the foam with silicone and pack substrate/rocks into the silicone.  

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On 5/12/2024 at 9:02 PM, OnlyGenusCaps said:

I feel like while that statement does not surprise me coming from you,

Yes it does, sorry for the delay but had to find a photo


We host a neighborhood Halloween party/hayride.

So the this will be easy plan for our screened in porch, take a piece of PVC pipe, cut it into 3 pieces then squirt foam into to it from both sides. Once cured, cut the smaller candles from it. I quickly discovered the foam did not cure inside the pipe and would start expanding once cut. It was a bloody mess. Note: a hot glue gun was used to create the dripping wax effect. But they came out great, there are over 30 candles hanging.

What I should have used,  two-part liquid, expanding rigid urethane foam.  Once mixed together, this stuff will cure anywhere. I use this for my much delay Mbuna condo project:


I made platforms for the rocks and placed balloons filled with sand on the base. I poured 3# density urethane foam around them. Remove the balloon and now I have condos for the Mbuna. I will set this tank up after our 3 week vacation in July. 

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You are a bottomless pit of creativity and ingenuity, sir!  Annoying as they may have been to create, those are some sweet looking candles!  I wish I had neighbors like you!  My neighbors are fine.  But this is next level! 

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