Unknown (To Me) ACU Trousers

Good morning.  Trust everyone had a good Christmas and the New Year has started out well.  

Picked up two sets of these in a pile of ACU trousers.  I've handled quite a few ACUs over the last few years and have never seen these before.  What are they?  My initial thought as I was quickly sorting through the pile is I had picked up some Goretex trousers.  Closer examination led me to believe it was part of a layered/level ECWS type of kit.  Aviation?  Cold weather over trouser?  The NSN and contractor number seem legit when I looked them up.  They feel like regular ACU material to the touch.  Doesn't seem to be anything different material wise.  

What are these?  Are they significant? Collectible?  Rare?  Not rare?  Any value? Someone enlighten me please!? Thanks.

Very interesting piece. The pants are standard issue, just heavily modified. I would assume to remove with ease if it got to hot. Also they are the wind resistant poplin, which are less common then the 50/50 NYCO ripstop. I got a SF grouping a while back with a poly pro base layer bottom modded the same way, he said it was a common thing to get done with guys going through ranger school so they could be removed easy when it got warm. But in this case that wouldn't make sense since it is an over layer, not really sure, maybe some others on here have some better ideas.

Interesting. Never considered that they could have been modified. Appreciate the info about the wind resistant poplin. Didn't know about that. In the grouping you bought were any of the poly pro tops modified in this way? I went back yesterday looking for modified tops but hadn't seen any. Plan to keep looking. Thanks.

No tops, those are easy to take off. Only bottoms were modded so that you did not have to take off your BDU pants and boots.

Makes sense except that it upsets the natural balance of the universe for Type A people like me - if there is a bottom their must be a top!

Failed to mention that both sides are velcro.