Microballons

[Jaynew]

I'm having trouble getting the right % of microballons. Was wondering if anyone could help me with a rule of thumb on the % to use. Making a 5 inch swimbait.

[DaBehr]

Do you mean micro-balloons as in the white "powder" that can be used to make plastic float???

If so, be advised that micro-balloon are a significant lung irritant (hazard) and should be used with extreme caution.

Personally, I would never use them.

Some info:

http://www.tackleunderground.com/community/topic/26222-safety-with-resins-and-micro-balloons/

...microballoons are borosilicate glass and when inhaled chronically can cause silicosis (permanent scarring of the lungs). I work in the abrasives/grinding industry and have personally viewed ceramic dust under a SEM, and have seen many particles often as small as 1 micron by 4 microns. Hence, your dust mask and/or filter is not removing them. When you sand microballoon filled resin your dust mask is not enough. 

[Stinky Finger]

*WARNING! What DaBehr said, microballoons/microspheres are some nasty stuff. Usually seen as a paint additive and also as an epoxy filler. Should be treated as asbestos dust and avoided like the plague. I recieved training on this stuff in Marine Corps aviation maintenance and later at aeronautics school, it is bad news. Just like asbestos dust it finds its way into the avioli of your lungs and cannot be expelled resulting in mesothelioma. IMHO it should not be available to the general public and limited to licensed personel with proper PPE. 

[Anglinarcher]

https://www.alumilite.com/resins/microballoons/

This will give you a good guide.  I don't agree with the warnings, at least to the extreme they are claiming.  Read the Safety Data Sheet yourself and take precautions as necessary.

Because I don't know the weight of your hardware, start on the higher side of amount to use.