Years ago I shared a flat with a guy who developed the squeezable ketchup bottle. Now this was a clever bit of plastics work - something like 7 layers involved in it. The problem is that polyethylene alone is permeable to water vapour, which isn't a good thing for ketchup. I was working for the phone company at the time, where polyethylene cables are lined with aluminium foil.
So when I threw away 2/3rd of a bottle of Balcotan PU glue, I took steps to avoid its successor going the same way. I wrapped the squeeable and probably permeable bottle with aluminium foil. So far this bottle has lasted twice as long as the first and hasn't set in the bottle. Inside the nozzle cap though, where I haven't installed a moisture barrier, it does go hard if I don't use it for a while.
On top of that good idea... refrigeration will double the shelf life of the poly glue that's been opened. Just make sure you have SWMBO's approval before you do it.
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