Best puddy?

[Richard Bartrop]

Milliput is good, especially if you're trying to sculpt some custom body work.  It models like clay, doesn't shrink, binds tight to a surface, so blending it with the surrounding plastic isn't a problem, and it's strong enough that you can make something with a fine edge without worrying about it crumbling.

[johnyrotten]

I've seen the bondo brand spot putty mentioned here, I assume a higher end glazing putty would work out the same, yes. I ask because I have a tube left over from my last motorcycle build, and I'm sure it has a shelf life. 

[Mark]

With the two-part spot putties (as well as Bondo, which is a "more coarse" filled that is seldom used for model building), it's the catalyst (hardener) that goes bad way before the filler itself.  You wouldn't want to use "expired" material on a 1:1 car because of the cost of the paint going on top of everything.  But it can be used on a model, as it won't be exposed to weather or other conditions. 

Before mixing a batch of "expired" filler, you'd mix the "filler" half, by itself, with a clean mixing utensil, then get some new catalyst.  All of the two-part spot putties I know of use the same catalyst. You can get new tubes of just the catalyst at Home Depot or Lowe's (or Menard's, whatever is in your area).  Mix a small batch of it, let it cure, if it is mixed correctly but doesn't cure properly then the "old" filler is no longer any good.

[rattle can man]

One thing I noticed with Bondo glazing putty is a chopped top on a '65 Pontiac I built 20 years ago has shrunk and you can now see the seams. And as for 2-part putties, If you use a product that is not proven by other modelers, test it on scrap before you use it on your model. I one tried regular 2 part automotive filler (maybe 35 years ago, so maybe chemistry has changed.), and as it cured, it created enough heat to warp the hood.

[NOBLNG]

Fine white Milliput is my favourite filler.

[Brizio]

I use a lot on my models and work props Perfect Plastic Putty. Superfine, doesn't smell, and dry very quick. 

[peteski]

Any 2-part putties which harden by chemical reaction will release heat while they set. Even Milliput epoxy heats up as it sets.  The faster the material sets up, the more concentrated the heat will be.  Bondo sets in just few minutes, so the heat is much more concentrated when being released in that short time. Milliput takes hours to harden, so the heating will be spread out over that time, never getting really warm.  Also the thickness of the material makes a difference.  The thicker the material is, the more heat is generated in that area.