The invention relates to a polymer foam having a density in the range between 5 and 120 kg/m
3 , containing a) a polymer component, containing at least one styrene polymer, b) 0.1 to 5 parts by weight (relative to 100 parts by weight of component a)) of a flame retardant mixture, containing b1) at least one phosphorus compound of formula (I) having a phosphorus content in the range between 5 and 80% by weight, relative to the phosphorus compound, (X
1 )
s =PR
1 R
2 R
3 (I), where the symbols and indices in formula (I) have the following meanings: R
1 is C
1 -C
16 -alkyl, C
1 -C
10 -hydroxyalkyl, C
2 -C
16 -alkenyl, C
1 -C
16 -alkoxy, C
2 -C
16 -alkenoxy, C
3 -C
10 -cycloalkyl, C
3 -C
10 -cycloalkoxy, C
6 -C
10 -aryl, C
6 -C
10 -aryloxy, C
6 -C
10 -aryl-C
1 -C
16 -alkyl, C
6 -C
10 -aryl-C
1 -C
16 -alkoxy, SR
9 , COR
10 , COOR
11 , CONR
12 R
13 ; R
2 is C
1 -C
16 -alkyl, C
1 -C
10 -hydroxyalkyl, C
2 -C
16 -alkenyl, C
1 -C
16 -alkoxy, C
2 -C
16 -alkenoxy, C
3 -C
10 -cycloalkyl, C
3 -C
10 -cycloalkoxy, C
6 -C
10 -aryl, C
6 -C
10 -aryl-C
1 -C
16 -alkyl,
C
6 -C
10 -aryl-C
1 -C
16 -alkoxy, SR
9 , COR
10 , COOR
11 , CONR
12 R
13 ;
R
3 is H, SH, SR
4 , OH, OR
5 or a group 30 -(Y
1 )
n -[P(= X
2 )
u R
6 -(Y
2 )
n ]
m -P(= X
3 )
t R
7 R
8 ; or two groups R
1 , R
2 , R
3 together with the phosphorus atom to which they are bound form a ring system; X
1 , X2 and X
3 are independently of each other identically or differently O or S; Y
1 , Y
2 are identically or differently O or S; R
4 , R
5 , R
9 , R
10 , R
11 , R
12 ,R
13 are identically or differently C
1 -C
12 -alkyl, C
3 -C
8 -cycloalkyl, which is unsubstituted or substituted by one or more C
1 -C
4 -alkyl groups, C
2 -C
12 -alkenyl, C
2 -C
12 -alkinyl, C
6 -C
10 -aryl or C
6 -C
10 -aryl C
1 -C
4 -alkyl; R
6 , R
7 , R
8 are independently of each other identically or differently C
1 -C
16 -alkyl, C
1 -C
16 -alkenyl, C
1 -C
16 -alkoxy, C
1 -C
16 -alkenoxy, C
3 -C
10 -cycloalkyl, C
3 -C
10 -cycloalkoxy, C
6 -C
10 -aryl, C
6 -C
10 -aryloxy, C
6 -C
10 -aryl-C
1 -C
16 -alkyl, C
6 -C
10 -aryl-C
1 -C
16 -alkoxy, SR
9 , COR
10 , COOR
11 , CONR
12 R
13 ; n is 1, if Y
1 or Y
2 is O, and 1, 2, 3, 4, 5, 6, 7 or 8, if Y
1 or Y
2 is S; m is a whole number between 0 and 100; s, t and u are independently of each other 0 or 1; and b2) elementary sulphur.