Heavy Foam is a trade-off gear perk that improves blast defense but slows your movement. It makes you tougher against explosions at the cost of speed.
Explosions do less damage to you, but you move slower. It works better for holding a position than running around.
Only if blasts are your main problem and you fight from cover. Most players will prefer Heat Stress or Major Blast Protection.
Steel Plate pieces with Major Blast Protection stack more explosion resistance.