| So far in my games the closest thing to being tied up I've had was one of the characters captured by the bad guy so the rest of the party had to go save her, and when they found her she was chained to the wall.
I ruled that as Restrained (seeing how the chains were about 3 feet). The player felt chained up and nobody complained, so I figure that worked well.
I would like to add, though, that rendering the players helpless is rarely "fun" unless they're freed fast or can free themselves relatively easily. Sitting around and having to figure out what obscure plan you've detailed for them to discover to free themselves is boring and often considered railroading. | 
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