That's the pen. It's available at practically every fabric store in America. I don't know if only one company makes them or not, but they're all purple. There used to be a light blue one, but I haven't seen that in years.

I've been using them for this purpose for close to 20 years, repeatedly on regular maps, with absolutely NO problem. I've never seen the ink color return. I don't see where they would be a problem on other paper, either, but I don't think I've used them on other types.

They are intended for fabric, and work well on that, too, although I think I've only used them on cotton and cotton blends.

Sue

Now THAT is the "cool idea of the month"! I'm gonna have to get me one of those disappearing ink pens for sure.

I waterproof all my maps. Either with a liquid application or contact paper. I do like Adventure paper. I will have to try MyTopo. Never used that.

Not only do I use the standard maps, if I am going to be in a National Park area, I research other trail guides for maps and route specifics, copy them and carry with me.

If I know where I am going to be hiking I put a 'handrail' on the map so if I get lost I can head in a cardinal direction to a safe place or logical S&R area that runs the length of my trip like a road,main trail, train track or river.

I also leave a copy of my map with someone so they know my route.

I love using alcohol based map pens and mark up my maps before and during my trips.

Man, I need to get a new map for my collection.

About the map collection Comms.
For years now I have been storing maps in white plastic drain pipe.
It is fairly cheap and pretty durable. The caps cost more than the pipe did last time I bought some.
I can roll and stuff a lot of maps into a 4" plastic tube.
With the caps on the tube the map rolls can sit in the back of a closet or in the shed rafters with no worries about them getting torn or mulched by mice.

What I have been thinking about for quite some time and what I want to do is to map my surroundings and search for the hiding places and shelters that can be used in a case a storm is chasing me. For example it would be useful for biking. When you see or hear a storm in the distance or just thunderclouds it´s good to know where to hide and that the shelter can actually protect you from the lightning. Especially if you happen to be far from home. Being close to your bike let alone riding it in the storm is suicide. So I think having the markings of "stormproof" shelters (bridges, ...) in the map would be very useful. And not just for biking.