The present disclosure provides peptide compositions (e.g., of self-assembling peptides) with particular attributes (e.g., peptide identity, peptide concentration, pH, ionic strength [including salt identity and/or concentration), etc. that show particularly useful material properties. The present disclosure also provides technologies for selecting and/or formulating particular peptide compositions useful in specific contexts. In some embodiments, provided peptide compositions have an elevated pH within the range of about 2.5 to about 3.5 and/or an ionic strength that is above that of a corresponding composition of the same peptide, at the same concentration, in water, but is below a critical salt point for the peptide (e.g., so that the composition is not cloudy).