Sealant Foam that is, the sort you use to close off hull breaches...
I just finished a quick conversion for a Sealant Foam Gun, aka Webber or Web Gun for one of my Salvage crew members with a slab-shield and wanted to share it with you. (I've yet to decide what the slab-shield will look like though...)
Here she is:
Just a quick conversion using the Cadian flamer, a Space Marine flamer canister and the (inverted) nozzle from a Chaos Space Marine vehicle accesory combi-flamer. I think it looks unique and identifiable to read as a Web Gun instead of a flamer.