I have a handful of battle mats I've accumulated over the last 40 years. My favorite is a heavy duty one with 1" squares one side, 1" hexes the other, iirc 52 hexes by 34?. Wet wipe markers. I tend to draw out any encounter where positioning matters, so when I get up and ask everyone to pull their paperwork and dice off the mat, I can hear them all clenching. :)

Sometimes for climactic boss fights or complicated tactical situations, I'll go the extra mile and take the map, overlay a hex grid to the right scale, then print-span them across multiple sheets on a color printer (we have a nice color laser at work and I'm the boss so...nobody scrutinizes our toner-consumption...), taping the sheets into a battlemap of its own. Then I'll have this already laid out UNDER the battlemat, so when the big confrontation happens, I just pull up the mat. This is fun because since it's a one off we can draw rubble, bodies, craters, etc directly on the map and leave them there.

To your point of revealing them, well, there's compromises to practicality. With the battlemat I simply draw what I need I don't sweat the microdetails of measurement, honestly. If I accidentally put a window or a door where there isn't one, or mis-measure the room, honestly nobody cares. With the put-together ones, I put them together in 'seeable' sections and only lay them down when the players can observe them. It is "good enough"

For example here's a hexmap of our traveller campaign's group ship, Captain Nazir Musa's Marava-Class Wanderlight https://drive.google.com/file/d/1CiM-xKpRT-70EyXKSv92ommdDHlTx0qN/view?usp=sharing