Buy sturdy rope nylon or polyester based.
How to secure a mattress to a roof rack.
I am planning to strap the box springs to the roof rack on my rav4 and tie them down with a bunch of rope.
If you purchase a new mattress to take home or are in the process of moving the mattress should be thoroughly tied down to prevent it from flying off the roof of your car and endangering other drivers.
Prepare to secure your load to the roof rack.
Put a piece of rope on the roof of the car that goes from back bumper to front bumper.
Toss the first long piece of rope over the length of the mattress.
A simple ratchet strap works best.
Put the mattress on top of the car and rope so that it goes length wise with the length of the car see pics above.
Secure your mattress to the top of the car.
The wind from the roads or highway can easily rip through the plastic if it is not properly secure.
This will stress any knot no matter how securely tied.
Still there is a basic method to follow when tying a mattress to the roof of a car.
Mattresses are large bulky and can pick up resistance from the wind.
Place the mattress on the roof making sure it s in the middle.
A ratchet strap ensures that the mattress will not flay away while driving especially if you do not have a roof rack.
There should be enough to secure one end under the front of your car and enough at the other end to secure the second end under the back of your car.
Center the mattress in the middle and put the rope over the length of the mattress.
If you do secure your mattress to a roof rack or safely in the bed of a truck strap it down with ratcheting straps.
Your owner s manual should say how much weight you can carry on the roof.
Ratcheting straps are much less likely to fail when moving a bulky item like a mattress.
I would say follow a similar process to what ryan said but i would not recommend using rope.
Secure the front end of the mattress and then the other end of the mattress.
After the mattress is secure in the plastic place the mattress on the roof.
Before securing the load to the roof of your car evaluate the item you will haul.