https://leadadventureforum.com/index.php?topic=75228.30

Clump foliage threaded onto a wire, gluing as you go. Then soaked in thinned PVA and left several days to completely dry out. I painted it by hand, the PVA surface seals the foliage so that it doesn't absorb paint. The PVA really provides a tough exterior; so far no damage or shedding at all.
What he said, basically.
What I learned from making this....

...was that
1. Look at a lot of reference photos of what you are trying to do.
2. Rather than using green foliage is better to make and colour your own sponge flock by shredding a piece of neutrally coloured mattress foam in a mixer together with paint
3. Use black paint and PVA for the foam if you want a smokey detonation, yellow (or maybe white) if you want to make a streak of napalm or dragon fire
4. I must admit that my blast above has not held up ideally well to the ravages of time. I think Pauls (Overlords) suggestion to apply a generous amount of watered down PVA is what I would do now.
5. if you want to do tendrils of smoke emerge from the central blast, use bamboo skewers. Don't forget to paint them black.
6. I used a hot glue gun to fasten the foilage to the skewers
7. I really recommend painting the thing with rattle can and/or airbrush. I sprayed the above blast with a few passes of black, then a light zenith layer of grey, then white. For the "hot" center I use an airbrush with successive layers of white, yellow, orange and red and a few touchups of black where needed.
8. Question the good taste in adding a dead pathan and a torn apart horse in the bomb blast.