See if you like the results from the following script I wrote. I tested on a very simple case so it might be slow. But the resulting mesh should be better than the nParticle mess.

/////////////////////////////////////////////////////////

string $sel[] = ls -sl; $sel = listRelatives -type particle $sel; string $particle = $sel[0]; int $pNum = getAttr ($particle+".count");

///////////////////////////////////////////////

// DETERMINE ROUGH PARTICLE VOLUME

float $minX = 1000000.0; float $minY = 1000000.0; float $minZ = 1000000.0; float $maxX = -1000000.0; float $maxY = -1000000.0; float $maxZ = -1000000.0;

float $ppos[] = getParticleAttr -at position -array true $particle; for($i=0;$i$maxX) $maxX = $ppos[3*$i];

if($ppos[3*$i]<$minX)
    $minX = $ppos[3*$i];

if($ppos[3*$i+1]>$maxY)
    $maxY = $ppos[3*$i+1];

if($ppos[3*$i+1]<$minY)
    $minY = $ppos[3*$i+1];

if($ppos[3*$i+2]>$maxZ)
    $maxZ = $ppos[3*$i+2];

if($ppos[3*$i+2]<$minZ)
    $minZ = $ppos[3*$i+2];

}

float $cx = ($maxX+$minX)*0.5; float $cy = ($maxY+$minY)*0.5; float $cz = ($maxZ+$minZ)*0.5;

float $max = $maxX-$minX; if($max < ($maxY-$minY)) $max = $maxY-$minY;

if($max < ($maxZ-$minZ)) $max = $maxZ-$minZ;

$max *= 2;

print "IGNORE FOLLOWING ERROR\n";

float $rad[]; $rad[0] = getAttr ($particle+".radius"); int $rPP = 0; if( catch( getParticleAttr -at radiusPP $particle ) == 0) { $rPP = 1; $rad = getParticleAttr -at radiusPP $particle; float $rMax = -1; for($val in $rad) if($val > $rMax) $rMax = $val;

clear $rad;
$rad[0] = $rMax;

} $max += $rad[0];

// CREATE META BALL MESH...USING POLY CUBE

int $res = 2; // ADJUST THIS TO SET YOUR START RESOLUTION

string $cube[] = polyCube -w 1 -h 1 -d 1 -sx 1 -sy 1 -sz 1 -ax 0 1 0 -cuv 4 -ch 0; polySmooth -mth 0 -dv $res -c 1 -kb 1 -ksb 1 -khe 0 -kt 1 -kmb 1 -suv 1 -peh 0 -sl 1 -dpe 1 -ps 0.1 -ro 1 -ch 0 $cube[0]; scale -a $max $max $max $cube[0]; move -a $cx $cy $cz $cube[0];

// LOOP THROUGH VERTICES TO ENVELOPE PARTICLES string $pts[] = ls -flatten ($cube[0]+".vtx[*]"); for($pt in $pts) { float $p[] = pointPosition -w $pt;

float $min = 1000000.0;
float $p1[3];
for($i=0;$i<$pNum;$i++)
{
    float $pp[] = `getParticleAttr -at position ($particle+".pt["+$i+"]")`;
    if($rPP)
        $rad = `getParticleAttr -at radiusPP ($particle+".pt["+$i+"]")`;

    float $results[] = `angleBetween -v1 $p[0] $p[1] $p[2] -v2 $pp[0] $pp[1] $pp[2]`;
    float $angle = $results[3];
    float $hypot = mag( << $pp[0], $pp[1], $pp[2] >> );
    float $opp = $hypot * sind($angle);

    if($opp < $rad[0])
    {
        float $dist = mag( << ($pp[0]-$p[0]), ($pp[1]-$p[1]), ($pp[2]-$p[2]) >> );
        if($dist < $min)
        {
            $min = $dist;
            $p1 = $pp;
        }
    }
}

float $results[] = `angleBetween -v1 $p[0] $p[1] $p[2] -v2 $p1[0] $p1[1] $p1[2]`;
float $angle = $results[3];
float $hypot = mag( << $p1[0], $p1[1], $p1[2] >> );
float $opp = $hypot * sind($angle);
float $adj = $hypot * cosd($angle);
float $angle1 = acosd($opp/$rad[0]);
float $opp1 = $rad[0] * sind($angle1);
float $dist = $adj + $opp1;
vector $v = unit( << $p[0], $p[1], $p[2] >> ) * $dist;
float $x = $v.x;
float $y = $v.y;
float $z = $v.z;
move -a $x $y $z $pt;

}

You can create a mesh from nParticles. See here.

You still have to go through the particles stage of course, and that makes it pretty slow. It would be nice if there was a tool to make an iso-surface direct from meshes, or curves.