Investigating 3mm Filament for the SumPod

I'm thinking of sourcing the parts (initially just the tubing) to use 3mm filament with the SumPod.  The trouble was, I didn't know the exact dimensions of 3mm filament.  Checking the wikis and reading through various blogs, I was none the wiser of the elusive dimension (or my search skills have abandoned me) and hence the required tube size.  Was the filament less than 3mm in diameter?  If so I could use a metric 3mm PTFE tube or was it actually 3mm, and require an imperial 3/16" (3.2mm) inside diameter tube?

Not getting anywhere fast I decided to buy some.  Specifically some PLA filament from Fabadashary.co.uk (no affiliation).