What is the difference between a volleyball for indoor courts and a volleyball for outdoor or sand courts?

I recently started playing sand volleyball and the balls seem to be very different. Any one know what makes a volleyball an indoor ball vs. an outdoor ball?

outdoor balls have in general always been heavier, thicker ... I assume it's due to, playing outside, the ball needs to be able to handle the elements better. sand, grass, rocks etc etc.

The beach volley-ball is softer (lower internal pressure) and slightly bigger than an indoor volleyball.
http://en.wikipedia.org/wiki/beach_volle...
Ball dimension is the same.
Weigh is different.
Internal air pressure is lower for beach ball.
outdoor ball is heavier and has less air pressure. This is so the wind can't push the ball as much and to slow the ball down a touch due to only having two players a side. Indoor ball is clearly the opposite.
i think an outdoor ball has to be a little bit heavier than an indoor ball so that it doesn't float or move much in the wind or outdoor weather.

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