Its Blu-Tak in Australia and the kids here in canada call it sticky tak. Its the stuff you use for putting posters on the wall and I have seen modelers use it for camo masking. I tried it once and it worked great for the mask, but it left little bits of itself on the kit which took a good couple of hours to remove. Is there a way to not have it stick to the plane?

I use White-Tac, from the same people that do blue-tac... It's a bit less sticky.

The easiest way to get rid of blue or white-tac is to get a big 'blob' & roll it over the recalcitrant bit.

It helps if you put the model in a bag & pop it in the freezer for a hour, it gets less grippy when cold.

Thanks i'll give it a go.

To avoid any marks on flat surface and ease removing white tac I first apply one layer of clear gloss on base color

Ditto that! I haven't ever had to stick it in the freezer though, just pulled it off with another little glob. It always seems to leave a bit behind, the first few times you use it. Over time though, as paint gets mixed in, that problem goes away. Once it gets to where it doesn't want to stick anymore, add a little bit of new stuff to it. I have about a golfball size glob that have had for years. Once old, it helps to knead and stretch it for a few minutes to warm it up a bit, then it'll stick good.

Like Jon, I'm a regular user of white-tack (Pritt sticky tac) as well. From what I've heard, the regular blu tac can leave greasy stains more easily.
The sticky tac can also leave marks, but I've only had those on surfaces painted with flat paints and when the sticky tac had been left in place for longer periods of time, like several days. The gloss before decaling got rid of that though.
Never had a problem with it sticking to the surface. Whatever small pieces possibly remain after removal, can be rolled over with piece of tac, as Jon already mentioned.

Thanks for all the replies.

I have not done a lot of camo and need a way to do mask it easily. Tac seems to be the most used.