To actually see if it is possible to super-pressure mylar/foil balloons - this requires more balloons (of the same size) and a lighter payload. Launching would need a quicker ascent rate and an earlier launch time to make use of the solar heating.
$$Callsign, count, time, latitude, longitude, altitude, lock, no of sats, nav status; tx mode; batt voltage; ext temp *CRC16
Overall the launch went well, filling the 4 balloons was easy, a pleasant change from worrying about damaging the balloon we were able to put the balloons in the boot of the car while we filled the rest. The payload also worked as planned and so once all was rigged up we released the balloons and payload. The ascent rate was slow but steady and we had good reception from multiple stations - at times up to 12 stations were decoding and uploading the data to the server.
Just after midday the balloon began to descend at approximately 1m/s and was tracked all the way down to 155m near to Rugby. As this was only an hour away by car I went to recover - arriving in the last known position I could pick up the radio strongly and after decoding the landing spot proceeded only to find it stuck in a high tree. On inspection it was possible to see that one of the balloons had burst and this had resulted in the slow drift down. The payload was too high to recover so I left my number at the local pub and went home, I also emailed some of the local hams. M0NWY kindly went to look the next morning and reported that it wasn't in the tree any longer and I then received a phone call saying that someone had found the balloon as it had come lose and drifted west. I was able to collect the payload in good condition the following Friday.