Green Building Forum - Backer Rod - anyone here use it? Difference between open and closed cell? Mon, 25 May 2026 08:51:22 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304497#Comment_304497 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304497#Comment_304497 Tue, 05 Dec 2023 20:16:36 +0000 greenfinger
Got plenty of caulking and filling coming up... I'd not heard of backer rod until recently, and having read up a bit on it it seems there's many others who are unaware of it. The big name stores don't seem to sell it either, which made me wonder how commonly it's used...

So, any fans of backer rod here for use in channels, chases, etc prior to caulking?

On a more technical note, there's a fair bit of online chat RE open vs closed cell. Apparently, open cell is more pliable/flexible and better for squeezing into gaps but not good if it gets wet. Also, they say closed sell off gases when cut or torn which can cause problems and even cause the caulk to bubble. But that's mainly from US sites/forums. Here in the UK, there's not much talk of it and the shops that do sell it seem to just sell "standard" stuff (which is closed cell). Does anyone know anything about this open/closed cell business?

Cheers]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304503#Comment_304503 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304503#Comment_304503 Wed, 06 Dec 2023 12:09:27 +0000 djh Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304505#Comment_304505 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304505#Comment_304505 Wed, 06 Dec 2023 12:18:18 +0000 Jeff B
Sorry therefore that I cannot shed any light on the different performances of open vs closed cell. However I would be surprised if the amount of released gas from closed cell would cause caulking to bubble, especially silicone, as this is very tough stuff when cured (which happens pretty rapidly).]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304515#Comment_304515 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304515#Comment_304515 Wed, 06 Dec 2023 17:03:01 +0000 Peter_in_Hungary Posted By: Jeff BI've never heard of "backer rod" until I read your post. Looks useful stuff and when I think back it would have been very useful for some jobs!
Me neither.
Having read descriptions of it I recall my father using twisted up newspaper for a similar purpose - certainly as a cheaper solution even if such commercial items were available 60 - 70 years ago. (I have also used twisted newspaper for the same purpose without any detrimental effect).]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304517#Comment_304517 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304517#Comment_304517 Wed, 06 Dec 2023 17:10:56 +0000 revor Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304518#Comment_304518 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304518#Comment_304518 Wed, 06 Dec 2023 17:45:50 +0000 Jeff B Posted By: Peter_in_Hungary
Posted By: Jeff BI've never heard of "backer rod" until I read your post. Looks useful stuff and when I think back it would have been very useful for some jobs!

Me neither.
Having read descriptions of it I recall my father using twisted up newspaper for a similar purpose - certainly as a cheaper solution even if such commercial items were available 60 - 70 years ago. (I have also used twisted newspaper for the same purpose without any detrimental effect).

Newspaper is still my default choice for indoor filling jobs!]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304536#Comment_304536 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304536#Comment_304536 Fri, 08 Dec 2023 12:52:36 +0000 greenfinger
Funnily enough, I have found bits of newspaper as described from old repairs by previous occupants and wondered what that was all about! I thought it was the sign of some short-cutting bodges, but perhaps it was a more common technique than I gave it credit for!

FYI, having spoken to the manufacturer he says to allow time for it to off gas if being cut or punctured before adding any sealant, but doesn't state why.

Very interesting that so many people have never heard of this stuff and yet for those that have they seem to think it quite indispensable. So much so that some of the suppliers only sell the smaller diameter stuff in reels over a kilometre long!!]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304545#Comment_304545 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304545#Comment_304545 Fri, 08 Dec 2023 21:53:20 +0000 djh Posted By: greenfingerSo much so that some of the suppliers only sell the smaller diameter stuff in reels over a kilometre long!!I don't know about a kilometre but ISTR I have a large box full of the stuff still left!]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304550#Comment_304550 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304550#Comment_304550 Sat, 09 Dec 2023 10:19:49 +0000 revor
https://sealnoseal.org/PDF/BackerRod/TechRevBackRods.pdf]]> Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304581#Comment_304581 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304581#Comment_304581 Wed, 13 Dec 2023 16:55:26 +0000 Osprey Backer Rod - anyone here use it? Difference between open and closed cell? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304598#Comment_304598 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18043&Focus=304598#Comment_304598 Thu, 14 Dec 2023 16:21:26 +0000 greenfinger