There are a lot of materials for fins.
If you are planning to launch your rockets at high speeds (lets say over 200 kmh) then you need very stiff, flat, and preferably light fins. If found that for these high speeds straightend PET bottle material, glued (sandwiched) together will do the best. The layered package is bit more heavy but very stiff and sturdy and almost indestructible. In the picture on the right you see this type of fin. The trick is to apply as much as pressure on the fins while the polyuretane resin hardens. The layered fin is almost transparent.
For lower speeds single layered PET material or styrofoam sheets of 2 mm covered with self adhesive plastic, like U use in cupboard will do also. For smaller fins (up to about 40mm span) you also can use a heavy weight paper (160 or 200 gr/m^2) on both sides covered with the self adhesive plastic. If you hear the fins rattle just after the air blowdown phase, when the rocket is at maximum speed, then you will know that they are not stiff enough. This phenomenon is also know as fin flutter. Your rocket will loose speed very quickly and the apogee height will be disappointing. The last material i tried was fins made from CD's they are straight, middle in weight and suited for high speeds, but compared to PET they are brittle and break off to easy at landing or when you have a lawn dart, PET fins have a high chance to survive a lawn dart landing especialy if you attach the fins with a clamping sleeve as i will show you.
The top picture on the right is from a double layered PET type span of 85 mm. The bottom one is of the styrofoam with plastic type span 40 mm. As you can see the fins have wrinkles caused this is damage caused through high speeds or the high acceleration. The fins are not stiff anymore. This will seriously decrease the stability of the rocket and increase drag a lot.
In the table below a comparison between the various materials. The given figures are far from absolute, but will give you an idea of their performance.
|
Material
|
Speeds
[m/sec]
|
Weight
|
Best size
|
Durability
|
|
Double layer PET
|
>60
|
heaviest
|
Large fins
|
Almost indestructible
|
|
Single layer PET
|
<50
|
middle
|
< 60mm span
|
Almost indestructible
|
|
Styrofoam
|
<40
|
very light
|
< 40mm
span
|
Careful handling
Damages quickly
|
|
Paper /
plastic
|
<40
|
light
|
<40 mm
span
|
Remarkable strong
Once damaged -> looses strength quickly
|
|
CD
|
>60
|
heavy
|
max 120mm
|
Not as strong, may break at landing
|
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