whats the best and easiest product to insulate between the joists - under floor boards on a first floor?

Foam insulation is great but is expensive. It can go into small places if you're not taking up the floor. If you have a professional do this, be prepared for a big price tag. If you're doing it yourself, buy the product by the case & make sure you have the time & patience to do between each joist.

For the best sound barrier at a reasonable cost, use rolled insulation between the joists. It's easier if you can remove & replace the floor. If there's a crawl space, lay this product between the joists from underneath. If you can't do this, see if there's a way they can blow insulation between the joists & flooring.

As for insulation, it won't make as much difference as you may think. A good carpet & pad will do about as much. Heat rises, so you won't be losing much through the floor.

~m~

hi, timber absorbs each and every of the pee, plastic makes a multitude out of the bedding. cord on the different hand the wee and fizz drop top through. No floor in any respect and bunny will dig and dig and dig. What different varieties of flooring is there? press board will give way after time, so will sheet rock. metallic yet lower back it is going to rust and make a multitude out of the bedding and could make bunny ill from the poo and pee. stable success....

If the floor is already laid then blown in foam insulation is the best choice. And if it isn't laid yet then wait till it's almost finished and use the blown in foam insulation.

http://www.foam-insulation-guide.com/expanding-foa...

just me again - totally agree