Without even passive vents? Which exact models?

I might need an additional laptop soon and would love to know about anything comparable to a MBP 13 retina but doesn't have any vents on the bottom.

The Thinkpad is the X201, and the HP was a DV2, an old model. They might have some small bottom vents, but they didn't have any problems cooling while sitting on my bed. Neither are probably comparable to an MBP 13, though.

Hmmm

https://support.lenovo.com/at/de/documents/pd025709

Don't think I'd be comfortable blocking those for extended periods.

I use my W530 on my couch frequently, with no issues. The main cooling happens in the back corner, where there are vents on both the side and the back. I'm not sure what the bottom vents are for, but blocking them doesn't cause issues even when I'm gaming.

Must be the tablet version, mine doesn't have those.

None of those are vents? What are you afraid of blocking the docking connector or the speakers?

Side vents are better than bottom vents, though macs have vents from top border of the keyboard. That's pretty ingenious design.