This trial is conducted in Europe. The aim of the trial is to investigate the pharmacokinetic (the exposure of the trial drug in the body) properties of FIAsp (faster-acting insulin aspart) in children, adolescents and adults with type 1 diabetes.

Inclusion Criteria:

• Male or female aged 6-64 years (both inclusive) at the time of signing informed consent
• Type 1 diabetes mellitus (as diagnosed clinically) for at least 12 months
• Body mass index (BMI) for children and adolescents (male and female) between the 3rd and 97th BMI percentile and for adults equal to or below 28.0 kg/m^2

Exclusion Criteria:

• Subject who has donated any blood or plasma in the past month or more than 500 mL within 3 months prior to screening
• Smoker (defined as a subject who is smoking at least one cigarette, cigar or pipe daily)
• Not able or willing to refrain from smoking and use of nicotine substitute products during the inpatient period