SPERX

Yes thats the stuff - it has a variety of Brand Names in the UK - most DIY stores have an own label variant but its all yellow, gooey and soluble in acetone. Bob clarifies my point about an escape path - it is essential that there is a route out of the wing for the excess volume of expanding foam to escape. I also think that the rate of expansion is affected by ambient temperature - the higher the temp the greater the rate of expansion. I have also used this stuff to fill vac-formed nose cones on EDF as well as filling in voids in polystyrene moulded fuselages on EDF models such as gear wells if I have junked the gear and gone for a hand-launch alternative - I fly off grass strips so EDF with gear is a non-starter.