A solution of a recombinant spider silk protein having a protein concentration of the recombinant spider silk protein of at least 100 mg/ml, wherein the recombinant spider silk protein, consisting of no more than 800 amino acids, is comprising a set of domains arranged according to the formula -REP-CT, wherein: a. the optional NT -domain, if present, consists of a sequence of 100 to 160 aminoacid residues derived from the N-terminal domain of a spider silk protein; wherein the NT- domain consists of a sequence having at least 50% identity to SEQ ID NO: 2 and/or at least 80% identity to SEQ ID NO: 1 or any one of the sequences in Figure 1; b. the REP -domain consists of a sequence of 30 to 600 amino acid residues derived from the repetitive segment of a spider silk protein; wherein the REP -domain is selected from the group consisting of L n L, L n AL, L n L, L n GL, LG n L, wherein n is an integer from 2 to 10; each individual A segment is an amino acid sequence of from 8 to 18 amino acid residues, wherein from 0 to 3 of the amino acid residues are not Ala, and the remaining amino acid residues are Ala; each individual G segment is an amino acid sequence of from 12 to 30 amino acid residues, wherein at least 40% of the amino acid residues are Gly; and each individual L segment is a linker amino acid sequence of from 0 to 30 amino acid residues; c. the CT -domain consists of a sequence of 70 to 120 amino acid residues derived from the C-terminal domain of a spider silk protein, selected from: a sequence having at least 70% identity to SEQ ID NO: 64 or any one of SEQ ID NO:s 62-65 or 67-73, wherein the sequence comprises at least 7 residues independently selected from K, R, E and D. a. the optional NT -domain, if present, consists of a sequence of 100 to 160 aminoacid residues derived from the N-terminal domain of a spider silk protein; wherein the NT- domain consists of a sequence having at least 50% identity to SEQ ID NO: 2 and/or at least 80% identity to SEQ ID NO: 1 or any one of the sequences in Figure 1; b. the REP -domain consists of a sequence of 30 to 600 amino acid residues derived from the repetitive segment of a spider silk protein; wherein the REP -domain is selected from the group consisting of L n L, L n AL, L n L, L n GL, LG n L, wherein n is an integer from 2 to 10; each individual A segment is an amino acid sequence of from 8 to 18 amino acid residues, wherein from 0 to 3 of the amino acid residues are not Ala, and the remaining amino acid residues are Ala; each individual G segment is an amino acid sequence of from 12 to 30 amino acid residues, wherein at least 40% of the amino acid residues are Gly; and each individual L segment is a linker amino acid sequence of from 0 to 30 amino acid residues; n is an integer from 2 to 10; each individual A segment is an amino acid sequence of from 8 to 18 amino acid residues, wherein from 0 to 3 of the amino acid residues are not Ala, and the remaining amino acid residues are Ala; each individual G segment is an amino acid sequence of from 12 to 30 amino acid residues, wherein at least 40% of the amino acid residues are Gly; and each individual L segment is a linker amino acid sequence of from 0 to 30 amino acid residues; c. the CT -domain consists of a sequence of 70 to 120 amino acid residues derived from the C-terminal domain of a spider silk protein, selected from: